Well the Marvel Unit 1 conversion kit was used to set the last .22 bullseye record, so I think it can hang with the Hammerli/Pardini/FWB bunch.
My Marvel Unit 1 came with a test target of 0.9" group for 10 shots of Eley Target at 50 yards from a machine rest. That's pretty darn good. I don't have a machine rest for my Pardini, but I would wager it shoots about the same at 50 yards.
The biggest advantage to using the conversion kit is that you can stay used to the 1911 trigger/platform for shooting the rest of the bullseye match. Personally I like the ergo's of the Pardini SP a lot better, but the Marvel Unit 1 is very accurate.
As for the dedicated 1911/22's, no, they are not that accurate.