Been riding NX2-AT's for about 20 days now. My take:
1. Mine have always stayed down from day one. No "break in" required on this front.
2. One motion / one hand. I do it all the time. Bending you knee & ankle a little make this an easy one motion move.
3. If the highback was already locked in position, I would say yes, though I have never tried.
One very key factor in setting up this binding: There are two position options for the highback. I am wearing a Burton Tribute size 11 and my bindings are Large. They were shipped with the highback in the front postion. No matter what I did they actually pinched my heal. Moved the highback to the rear position, moved the cable to the back position, reset my straps and they are now BRILLIANT !!!!!!! Locked in, easy in and out and very, very comfortable.