Thanks for all the comments. Pulled the trigger on the Drift Ghost. Not very easy to get here. None of 10 shops I've contacted had any other helmet cam than GoPro or was even able to give me information on other brands. They've got kind of a monopoly... makes me a bit suspicious... either they are overwhelmingly better than the others OR it's a hipe/marketing thing like with the Apple stuff. Anyway, found a Drift in an online shop.
In two weeks I'll know if its waterproof enough for watersports without an additional case if it survived a week kite surfing