Multiple reviewers like the built-in mic because it stays out of the way, is always available, and makes the headset feel cleaner and more portable than boom-mic rivals. That convenience is real, but it comes with a clear quality tradeoff.
An inline mic is consistently included for calls and basic voice use, though the coverage says more about availability than exceptional call performance.
The built-in mic is usable and often better than expected for the price. Call performance ranges from merely okay in quieter spaces to impressively clear in stronger reviews.