I had a 9 and an 11 (when the 9 I lent to my jetski-ing mate ended up in Davy Jones’ locker 🙂 ). The 9 – as posted above – was a bit glitchy and would randomly lock up esp when warm. Meaning a battery out reset. I also suffered some odd file corruption and that was using recommended SD cards.
11 has been pretty good. Touchscreen is still horribly slow (12 is way better apparently) but stabilisation is brilliant even with the crappy bouncy chest mount. Only issue I have is low light performance is still average at best. If I replaced my 11, I’d go with another brand.
I’ve also fitted the media mod which massively cuts down on wind noise. Worth watching a few MTB GoPro set up videos as it’s easy to completely ruin the footage by getting the settings wrong. Also if you’re using a chest mount, get it low, looks faster 🙂