I have the CM-500 and in a very quiet room it's not bad at all. However, it does pick up "breath" noises and some background noise (if there is any).
The difference between that and a "real" communications headset is rejection of breathing noises, background noise and other stuff. Nothing like a cardiod pattern dynamic mike to minimize breathing sounds and background noise and maximize intelligibility.
On the air I can tell in two seconds when someone's using a CM-500 or similar.
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