Assisted opening is perfectly legal, they don't open "automatically by gravity or centrifugal force or by hand pressure applied to a button, spring or other device in or attached to the handle of the knife", you need to initiate the movement by moving the blade itself. I own a few assisted knives (ok let's be honest, a lot) that I bought locally and over internet. Some have been checked by customs and released without issues.
I own a few ZT and they're awesome (nothing to do with cheap kershaws), My ZT-0560 has to be the knife I carry the most.
Great, now I need to check out FOC and see if I need a new knife.