Obviously more than 10mph gust! That's a post that deserves to be read by every kiter in the world.
I'm sure every safety system has a potential mishap that can make it backfire. I've had the SAFE system on my WW snag in a way that instantly created a full power dive to one side only, with an almost complete lack of control resulting at full speed in one direction (in this case, the direction of the beach). Luckily, the QR still worked.
Plus, these safety systems probably give people more confidence to go out in marginal and potentially dangerous conditions.