Compare Dyson Purifier Big+Quiet Formaldehyde BP04 vs Alen BreatheSmart 45i

Durability evidence is limited but negative around the plastic finish, which one reviewer says can chip and scratch.

Durability evidence is favorable, including durable construction and a two-year owner report.

The remote is useful and magnetically stored, but one reviewer worries the tiny remote may get lost.

Remote control is mixed because the base model lacks it, while app-enabled units can be controlled remotely.

CADR evidence is mixed to negative: one reviewer wants a published rating, and another says smoke CADR is good but not exceptional for the size.

CADR evidence is positive overall, though some reviewers note stronger or cheaper competitors.

The app is consistently described as useful, slick, detailed, and easy to use, though one reviewer wanted broader reporting.

App support is useful when available, but evidence is mixed because some units lacked Wi-Fi or made app support unclear.

Odor reduction is strongly supported, including cooking smells, deodorant/aerosol odors, and general scent removal.

Odor reduction depends heavily on filter choice: upgraded carbon filters help, while the base filter leaves odors.

One customer reports receiving a refurbished unit despite saying it works well.

The only condition evidence is a strongly negative customer report of receiving a used, scuffed unit.

Most reviewers praise build quality and sealing, while one criticizes the plastic exterior as scratch-prone.

Expert reviews strongly praise the body, fan, filters, and overall construction quality.

Expert and customer evidence strongly supports effective purification, from quick pollutant reduction to broad whole-home confidence.

Most reviewers found the 45i effective at cleaning air quickly, though two customers reported poor or contaminated performance.

VOC reduction is a standout, with praise for detecting, tracking, and reducing VOCs and TVOC levels.

VOC reduction depends on upgraded filters; reviewers say the Pure filter is weak for VOCs.

Pollen evidence is limited but favorable through the reviewer’s HEPA particle-filtration assessment for seasonal allergies.

Pollen evidence is limited but positive from a customer connecting it to stuffy-nose relief.

Auto mode is useful and can ramp up when pollutants appear, although one long-term tester could not reliably replicate the automatic increase.

Auto mode is consistently described as responsive, handy, and useful for hands-off operation.

Value is mixed to negative: reviewers acknowledge premium performance but repeatedly call the BP04 expensive, pricey, or not a great value.

Value is mixed: several reviewers call it worth the cost, but it is not a budget pick.

Design draws strong reactions: many like the premium, unmistakable Dyson look, while some find it clunky, bold, or scratch-prone.

Reviewers like the discreet, customizable design and swappable front panels.

Evidence supports allergen reduction through reviewer testing and HEPA-related discussion of pollen, mold spores, and pet dander.

Customers and reviewers credited the unit or its HEPA filter with allergy, allergen, and mold-related benefits.

Sensors are generally praised as advanced and responsive, but one reviewer found some reaction times slower than expected.

The laser particle sensor drew strong praise for accuracy and responsiveness to changing air conditions.

Hidden wheels help on hard floors, but the unit is bulky, awkward, and harder to move over carpet or stairs.

Portability is supported by positive comments about the rear handle and easy movement.

Size is the most consistent physical drawback: reviewers repeatedly call it big, large, bulky, or overkill for compact homes.

Size is mixed: slim enough in depth, but still bulky compared with some competitors.

Reviewers praise strong, pleasant, large-room airflow, though one notes air disperses with distance.

Reviewers liked its airflow design and air movement, with one lab noting wind speed below average.

The small screen is useful for pollutant status and trend visibility, but its size and placement make it a secondary interface.

Display and control readability are praised, with one minor complaint about the Turbo label.

Overall satisfaction is high across experts and customers, with the main reservations centered on cost, size, and fit for smaller homes.

Overall sentiment is favorable, with strong expert approval and mostly enthusiastic customers despite two bad experiences.

Running filter costs are considered reasonable or low for this room size when spread over claimed filter lifetimes.

Filter cost is moderate: not the cheapest, but competitive when paired with energy costs.

Real-time monitoring is a major strength, with reviewers praising detailed pollutant graphs, current readings, and visibility into home air.

Real-time monitoring is repeatedly praised for clear feedback and quick detection.

Power draw is rated positively, especially measured low and high settings relative to the Dyson’s output.

Power consumption is low in operation, with a caveat about standby draw.

Mold-spore evidence is limited but favorable through the reviewer’s HEPA particle-filtration assessment.

Mold reduction evidence comes from praise for the HEPA filter's ability to handle mold particles.

Dust evidence is positive but less dramatic than odor or VOC performance, with one dust test creating only a slight change before returning to normal.

Dust removal is usually praised, but one customer said it did nothing for visible dust.

Long filter life is a consistent positive, though one reviewer cautions that heavy smoke use could shorten real-world replacement intervals.

Filter life is viewed positively, with filters described as lasting about nine months to a year.

The carbon filter is repeatedly tied to strong chemical, odor, gas, and nitrogen dioxide handling, with one reviewer calling chemical filtration best tested.

Upgraded carbon options are repeatedly praised for odors, VOCs, and smoke, but the base Pure filter lacks carbon.

Smart features are a strength, including app data, history, voice assistant support, schedules, and remote-style controls.

Smart features are useful but not central, with app tracking and Wi-Fi treated as modest extras.

Quiet operation is one of the strongest points, with reviewers praising low noise even at high airflow.

Noise is a major strength at low and quiet speeds, although higher settings are more audible.

Reviewers describe the multi-stage filtration positively, especially the improved three-step system and well-sealed filters.

The combined filter system and optional filter types are praised for matching different use cases.

Particle removal is strong in measured and experiential tests, including PM2.5 reduction, fog clearing, and HEPA particle capture.

Particle removal is strongly supported by lab tests and owner observations.

The HEPA H13 filtration and sealed filter path are viewed as high-grade, efficient, and important for particles.

HEPA filtration is praised as medical-grade or effective for small particles and allergens.

Filter access and replacement are described as simple, improved, and supported by app guidance.

Maintenance and filter access are generally easy, though one reviewer disliked the attached pre-filter.

Room coverage is strong for large and open rooms, but reviewers warn smaller homes may not make full use of it.

Room coverage is best for medium spaces; reviewers caution against very large rooms.

Smoke removal is positive overall, but one review says smoke CADR is good rather than exceptional for the unit’s size.

Smoke removal is good for particles, but stronger smoke/gas performance requires upgraded carbon filters.

Setup, controls, app pairing, and operation are repeatedly described as simple, intuitive, and easy.

Setup, controls, and filter access are repeatedly described as easy and intuitive.

The ten-speed fan controls and airflow angle options are useful for comfort and control.

Multiple fan speeds, including turbo, are useful and let reviewers balance cleaning and noise.

Energy use is praised as low relative to output, with one review calling measured wattage impressive.

Energy use is a recurring strength, with reviewers calling it efficient and low-cost to run.

True HEPA/H13-style filtration evidence is positive, especially sealed filtration and high particle-capture capability.

True HEPA evidence is positive, including long-lasting and independently verified H13 filter comments.

Reliability evidence is sparse but positive from one user’s history with Dyson purifiers not failing.

Reliability evidence is positive but limited, mainly from long-term ownership and brand support.

Adjustable airflow angles are useful for matching bedroom, living-room, and cooling needs.

Child lock and lock controls are presented as useful parts of the control layout.

The top-mounted, clearly labeled control panel is treated as convenient and easy to use.

Filter availability is a strength because reviewers note Alen still supports much older models.

Formaldehyde evidence is positive but partly sensor-based; reviewers note falling levels or normalizing readings after tests.

Handles are repeatedly praised for making the unit easier to move around the home.

Indicator lights are useful for status, filter condition, and air quality feedback.

Ozone evidence is reassuring, with zero or very low measured emissions and a disable option.

Pet-dander evidence is limited but favorable through the reviewer’s HEPA particle-filtration assessment.

PM2.5 detection is positive overall, with one reviewer saying the Dyson was ahead of a monitor and another observing a quick match-test response.

Pre-filter evidence is mixed: it catches larger particles but can be harder to clean than a separate pre-filter.

Replacement experience is positive because filter access is simple and the app can guide care and replacement timing.

Scheduling evidence is favorable but limited, mainly through the app’s simple scheduling controls.

Sleep and night-mode evidence is positive, with quiet operation and dimmed lighting noted.

VOC sensor evidence is positive, with reviewers noting automatic VOC display changes, detailed graphs, and good VOC readings.

Voice assistant support is noted favorably as part of the premium smart-control package.

Warranty coverage is seen as valuable, but it depends on registration and OEM filter use.