I initially put my gopro on my mask (cressi superocchio) but I do not use it anymore.. It's fine for shore diving or sticking to the shallows, but I found that it offered a bit of resistance when diving below 15m. On the way up it would cause the mask to wobble a bit. You can still see, but if you're thinking of that I'd rather use the head strap and put it under your hood.
I find the head mount a bit jittery as I tend to scan a lot. My next project is to mount my gopro onto an old freedivers handle of mine so hoping that works out fine.
You get some nice gun mounts as well, but apparently they can initially affect the aiming when mounted on the front of the gun. A lot of guys shoot like that so it should be fine after firing a couple of test shots to get your aim in.
Safe diving and I hope the above helps.