Had a USO, sold it for a NF. Much happier.
Had to send my USO back for debris in the ret and the ill knob was so loose, when you shot, your ret would turn off. Took roughly 1 month to get back. Wasn't impressed with that.
My 2 NF have been 100%.
Another thing I wasn't impressed with USO was how much $$$ they want to charge to change to a different ret. $400 + whatever the ret cost... Keep that in mind if you buy a USED USO, make sure it has a ret that you'll like, or you're screwed.