ahh, I have had the BM556 for a little over a year now and it's better than ever.
The lock becomes smoother over time as the parts wear-in with each other. I carry it EVERY single day at work, and at home, and have used it for everything for light prying, stripping/cutting wire, punching through thick materials, whatever comes along. The blade is as tight as ever. ZERO blade play vertically, and a small side to side play that I adjusted into the pivot intentionally so it'll swing out with no friction. It can be tight as a drum If I want it that way with a 1/8 turn of the pivot pin. Ive had no spring breakage either even with nearly constant flicking when Im not actually using the thing. The parts of the axis show virtually no wear at all other than a polished look. The axis seems equal or more resistant to failing under twisting loads than any other knife I own, not to mention more reliable with slick stuff on the mechanism, stronger, smoother, easier and just plain more fun to operate than anything I can think of offhand.
As a sidenote, the often-reffered-to-as-cheap Zytel handles show absolutley no damage or scratches even after falling off a loading dock in cold weather, being dropped a bunch of times on concrete floors, junk in pocket crashing into it for over a year, etc. Can't think of many materials that can claim that type of damage/wear resistance.