I'll put this here too.
520 is awesome! Buy one! But in all seriousness the springs in my 520 are still going strong after 6 years. I have 5 other axis knives and have not had any problems with the locks. Regarding the blade play it's just like any other knife that has a pivot. If you like a really easy free swinging blade than you will probably have a slight amount of play. I keep mine a little on the tight side just because I like to fully open the blade with my thumb on the stud. It is still very smooth and I can still flick it open really fast if I want, I just don't do it that way generally.
Also, $120-$130 is a pretty normal price from most online dealers depending on the blade configuration.