I have a PS90, and it's a great gun! Ammo used to be extremely expensive ($20-30 for 50 rounds), but now .223 is catching up and 5.7 stays the same price, so it's not that much more!
The 50 round mags, and the feel of a .22 (the ps90 is like shooting an air gun! it's damn fun) make ammo disappear that much faster.
They are fun, reliable, and easy to maintain (as well as being extremely ergonomic,, balanced, comfortable etc). Just make sure you don't overpay for one. Many places are selling them for around $1300 brand new now. If for nothing else, it's worth having because of the "cool" factor. I DO plan on short barreling my PS90 though...
