Replay XD 1080 is a tiny, light lipstick HD camera which mounts easily and unobtrusively on many headsets (e.g. above the left ear for right seat heli flying). I have used it that way for heli (R22 and R44) as well as FW flying, and it works great. You do need to adjust it to point the right way, but after a couple of attempts you should be fine and the adjustment remains stable.
I would also highly recommend adding a direct connection to the aircraft's audio. In my case, I am using a FW headset with a heli audio connector adapter, so I inserted a 2.5mm output splitter which then goes into a small digital audio recorder. This way I have two audio recorders: the built-in one inside the camera for "ambient sounds", and the digital audio recorder for very clear ATC and intercom conversations. (I merge the two audio channels with varying weights in the final editing).
Regarding the concept of heli training with video recording, it has been extremely valuable to me. I was able to review each lesson at home many times, and the solo CC flights were a pleasure to re-live at high res on a big HD screen.
I did turn the video off during my heli check ride in the 22, since I didn't want to distract or impose on the examiner.
I have chosen this after reviewing virtually all heli videos on YT, and feel (at least for me) this solution is optimal.
Overall I have been extremely pleased with the quality of both video and audio, and feel it has added immensely to my heli training and FW flying.
PM me if you'd like more details and sample videos.
Replay XD1080 HD Video Camera is the Best Action Camera.
Optional digital voice recorder that I use for intercom/ATC:
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