My buddy has the PS90.... Fun little gun, but it feels like you're shooting a .22lr. I don't know if I would trust my life with a round like that no matter what the specs say. In a pistol sure, but a rifle? I'll pass. Also, no iron sights so you pretty much have to get some sort of optics for it. The iron sights my friend put on his sucked ass. They're mounted so close to your face it's almost impossible to focus on the front post and still see your target... Bleh.
You might want to check out the FN F2000: .223, accepts AR-15 mags and the shells don't eject near your face. Trigger isn't half bad for a bullpup either. I've handled them in the store, but never had the chance to shoot one. If you have a choice, I'd skip on the integrated 1.5x (or whatever it is) scope and just use the rail to mount your own optics.
I got a Carbon15 from Bushmaster and that is one light, tight little rifle. Dropped a match grade trigger in it and a Trijicon scope and it just rocks... So much fun to shoot. Weighs around 6 lbs. The carbon fiber and heavy fluted barrel stays uber cool under heavy fire. Only downside is no forward assist. Well that, and that people bitch that it's a "plastic gun." Then I have to remind them that the "plastic" it uses is 40% stronger than steel.