I have a witness polymer fullsize .45 that came with the .22lr conversion. At first I hated it, the .22lr upper wouldn't feed ammo, I would have both FTF and FTE... I was lucky to get one full cycle. I found that the slide was hanging up on the frame, so I filed down a couple of burrs which helped a little and made 5 out of 10 rounds cycle... after a little more inspecting every thing, I noticed a wierd wear pattern on the firing pin block, so I took a video of me shooting to see what was going on. While playing it in slow motion I could see the slide hanging up on the hammer as the slide was kicking back to extract the round, which was causing the new round coming in to stove pipe. A little bit more filing and polishing and now have shot 500 rounds through it with out a single flaw. I am holding a group about the size of a quarter at 25 yards, and at 50 yards you can cover all ten holes with a half dollar.
Lat month I would have told you to stay clear of it, but now that I have done all the work, I see its true potential.