I also have a SIG522. Mine is the classic version, in black.
It has had just over 1500 rounds through it and only 4 failures: two light strikes and two stove-pipes.
Two things to look out for:
1) You need to make sure the gun has a shiny bolt, not the two-tone one with the rear half parkerized. That two-tone one is the old bolt with the tapered rod mentioned above.
2) There are some versions of the rifle being sold with a welded flash hider. If you want to put a suppressor on it, best specify that the rifle must have a removable flash hider.
Two things that are "features":
1) There is no traditional last round hold open. The bolt holds halfway open, against the magazine. If you take the magazine out, the bolt goes forward. There is a bolt stay, but it locks only if you pull the bolt all the way back.
2) The stock is a bit short, even if you use the fattest pad as supplied in the box. That's a minor gripe, but worth thinking of.
I am waiting for a suppressor to arrive, then I will test that. Currently I use this for standing 25 yard and 50 yard shooting, with a cheap Mueller reflex dot. It works very well.
I saw on Rimfire central that a guy took out the fake gas tube and replaced that with a green laser. Looked like an interesting mod.