Helmet is my favorite,
Line mount is cool but not super practical and can be dangerous
I don't really like mouth mount, it's usually a bit shaky, shoulders are in the way and annoying to carry around when not filming. Also when powered and choppy it's kind of hard to breath sometimes. I guess pro of mount mount is that you can do selfie, though you can also grab your helmet for selfie lol.
Anyway, some people love mouth mount others don't... Looks like it's personal choice.
you better change views for anything longer than 1 minute.
No one yet suggested pole in the water. It works great for shallow/flat spots. You can make one out of cheap telescopic window squeegee and also use it as giant selfie-stick.
If you have offshore flat spot, you can just leave gopro on the beach and do your stuff 3-10 ft from it..
Line mount is great too but I'd hesitate to use it in sketchy conditions.. It may screw up flagging of the kite.
This clip was filmed with mouth mount (biting on orange floaty) and placing gopro on the sand.
MIx it up is great just need more organisation, battery and possibly more GoPro. Also when wind is up I usually avoid line mount, i have been lucky so far with it but I wipe out plenty already with bad line wrap that I don't feel serene adding a line mount to those sessions.
In most case line mount will break if it gets tangle bad in powered conditions, anyway I would try to kite conservatively with line mount if you go for it.
I tried mixing it up a bit between 2 days in a row, first time on C kite with a lot of wipeouts