I bought 2 synthetic stocked .22's pre-owned from shops. 500mm from Baker and 600mm from UA.
Baker gun has been a great shooter right out of the box. UA gun had some consistency/repeatability issues and went back to UA for warranty repair (even included free shipping). It came back after UA replaced the reg, the valve pin, valve seat and valve seat o-ring, and now shoots great too. (I will never know whether this gun's condition/function was due to FX design/manufacturing, or (more likely in my mind) something done by the initial owner).
HOWEVER both of my DRS's shoot the first 1-2 shots after a break, mag refill, etc. a little slow, but then settle into nice and consistent shot strings. My 500 prefers 15.89's while my 600 likes the 18.13's better. I don't much like the FX OEM mags for these guns, but the Orion mags are fantastic. My guns have the M8 gauge threads, and M8 gauges are generally seen as being lower in quality and accuracy. For improved gauge accuracy at a reasonable price, both of my guns now have Sekhmet digital gauges, so I am confident in knowing my air cylinder's actual pressure.
Overall I really like them - light, handy, accurate, comfortable to shoot. They are loud out of the box so assume that you will need/want a moderator. Shots per fill are what they are, so these guns are better tethered when shooting off the bench, or when used as hunters where fewer overall shots are generally needed between fills.
Knowing what I know now, would I buy again? Definitely yes.