Got the upper for Christmas, finally assembled a lower for it. Have shot 1000 rounds through it in two different trips to the range. Using CCI minimags and BDM magazines, the first 500 I had a FTF and one FTE (stovepipe). Not too bad, especially for a new unit because they do require a break in. I left the gun dirty to see how it would continue with the next 500. All 500 fed and fired flawlessly. Groups were about 1" at 25 yards, and 2" at 50 yards from a bench (using a Primary Arms micro red dot). All in all it is a very decent little plinker that won't break the bank using it as a practice carbine in lieu of my AR15.
I know the haters are going to come in and say I could have gotten a S&W or Colt (Umarex) .22 for less, but I didn't want a cheap feeling plastic rifle, I wanted one that would replicate my AR15 carbines exactly, and that is what the Spike's does. The fact that it is 100% reliable after break in and has decent accuracy is a big plus. Anyway, for those looking for a dedicated .22 upper, the Spike's is a good choice. I have heard CMMG isn't bad either - if you can find one.
ETA - the upper is one of the lightweight ST-22's. I built it to look like another lightweight carbine I built (below the first pic).