It's an amazing PDW weapon. The accuracy is high. Tight groups with all ammo. The trigger is very usable. You can add your light, laser, and optic of your choice easy. The perfect sling is available for purchase. Mags are available and not pricey.
The downside? Ammo is still a dollar a round or more. And it is scarce.
SBRing is not straight forward. Either way you choose, you are damaging the factory barrel, just to remove it, chop or go with a replacement US made barrel makes no difference. This isn't like an Uzi where you unscrew a barrel nut and pull out the barrel.
I'm in the minority, but I don't really see the need to SBR the PS90 unless you were going to suppress it. The 16" barrel gives good boost in velocity and it's still a small handy package.
This isn't a legitimate downside, but loading the mags is a pain in the butt.