This does not make sense - the "one hand on the release when thumbs up, to save seconds"
In order to give thumbs up, you have to take either the hand on the QR away (thus the advantage is somewhat lost), or you have to let fully go of the bar, which is even worse
I only got two hands - I dont know about you ?
Having only one hand on the bar, typically the upper one, is also quite dangerous, as you can easily whip the kite into the powerzone.
So agree, that two hands is better, like Thor says.
Have seen some really ugly accidents happen, when relative new kitesurfers hold the bar with one hand instinctively, and let go with the other - thus you make a kiteloop or fly straight into the powerzone
Either you hold on with both hands, or let go with both hands - NEVER hold with one hand only, as when shit hits the fan because of a pilot error, you are really in deep shit
Of course, when experienced you can control better with one hand - but the errors made is often when not paying attention or the less experienced.
Thus I am not a fan for "one hand launches" in general.
Difficult, as one hand on the QR is faster, yes, but not possible either if you have to give thumbs up