Had mine since 2010. Great rifle, very accurate, and will run on just about any .22LR with or without lubrication. I have put many many bricks of Federal bulk and CCI through it, used to shoot it almost every day after work, and I really cannot think of any time it had any sort of failure - very reliable and unpicky for a .22. The only thing I have found it didn't like was Remington Golden Bullet, which would have an occasional FTE.
Mags are also easy to find from Black Dog, cheaper than most other "tactical" type .22s.
Controls and charging handle are usable with stock folded, and since it's .22 it's easily controllable with the stock folded as well, especially with a red dot sight installed.
If I was going to buy a tactical style .22LR today it would probably be a 15-22 just because of the huge aftermarket, but the 522 is just a very solid rifle, I don't feel that it needs very much if anything. Great trigger, good ergonomics, great magazines. I greatly regret not going in on the deal back in those days where you bought a Sig 556 and they threw the 522 in for free. Oh well.
Quote History
Did you use a real Sig stock or is that one of the airsoft ones? I have heard of people using the airsoft stocks and filling them with fiberglass resin to make them a little more solid. The adjustable stock is the only thing I really don't like about mine.
Wish I had the SBR version! Looks like it would be a great backpacking rifle and would fit into most day packs. The normal length one will but you get a bit of barrel sticking out of the pack.