Well my M10 shit the bed the other day.
I plugged it in to charge and nothing happened so pulled the lead out and the socket (which should be soldered to the circuit board I side I presume) came out with it.
After that it was intermittently refusing to switch on, switching itself off etc.
Contacted Banggood about it and after I sent them a video of the problems they have said they'll send me out a replacement so I'm pretty impressed.
Re helmet mounting, check out some youtube vids that have been shot from different mounts. I think helmet mount gives the most boring and unengaging viewpoint. Chest mount looks best I think but my experience with a chest mount has not been so great, difficult to get the angle right and either end up with the camera pointing at the floor when I get out the saddle or at the sky when I sit down.