I'm torn.  I bought this for the great reviews, however...
Nearly everyone says I am muffled or hard to hear when it's in my ear.
If I take it out of my ear and put it in front of my mouth, no problem.
I tried resetting factory defaults, turning off the noise cancellation and other settings to no avail.
However it is very light and A2DP compliant so I've been using it to stream MP3 audio while I mountain bike.
It works pretty well, the audio quality in the speaker is very good.

I am using this with a Nexus 5 on Kitkat 4.4.4 which may be part of the mic audio problem.
However I used to have an old Sony BT headset and never had anyone say I was hard to hear.
I'm torn. I bought this for the great reviews, however... Nearly everyone says I am muffled or hard to hear when it's in my ear. If I take it out of my ear and put it in front of my mouth, no problem. I tried resetting factory defaults, turning off the noise cancellation and other settings to no avail. However it is very light and A2DP compliant so I've been using it to stream MP3 audio while I mountain bike. It works pretty well, the audio quality in the speaker is very good. I am using this with a Nexus 5 on Kitkat 4. 4.4 which may be part of the mic audio problem. However I used to have an old Sony BT headset and never had anyone say I was hard to hear.