For someone who has practiced using their QR to the point where they can activate it in the shortest amount of time, and who is specifically prepared to do so as in a launch situation, keeping one hand on the QR would probably save an insignificant fraction of a second in the event of a problem.
Personally, I believe that having 2 hands on the bar usually provides significantly more control than one hand and that the advantage that this potential control provides generally overcomes any disadvantage that might accrue due to the above described lost fraction of a second.
It seems to me that the 1 hand technique puts more reliance for preventing an accident on the functionality of the QR while the 2 hand technique puts more reliance on kite control
while still having the benefit of the QR as backup. Since NO QR can be GUARANTEED
to work as intended when needed, it seems better to not depend upon it more than absolutely necessary.
However, it should be noted that some people with some kites can exert more kite control holding the bar in the center than other people with different kites (especially where greater bar pressure is found) so the degree of difference between the 2 methods can vary from case to case.
Malibu Kitesurfing - since 2002
(310) - 430 - KITE (5483)