I can tell you that the Kimber .22 conversion that I bought, used, for a Colt Gold Cup shoots straighter than the road to hell, and has been entirely reliable with good ammunition (CCI's) and even works well with Federal bulk pack stuff for autos.
The package also shoots extraordinarily straight.
There is apparently some challenge in getting the slide stop to engage with magazine actuation, so it doesn't work that way on the Kimber. However, a 'dry snap' on an empty chamber is supposed to hurt nothing whatsoever.
If my experience is any guide, get the Kimber and have done with it.
Moon

I had the same questions and after shooting a friends Kimber Conversion I decided to go with Kimber. After having my 22 conversion for 6 months I can say I love it. I put my Kimber Gold Match in my machine rest with the conversion and tested several brands of 22 ammo. So far the CCI Mini Mag gave me the best 1-1/8 " ten round groups at 25 yards. That's plenty good enough for me. Additionally, the Kimber is not picky about ammo as long as it is high velocity. Standard velocity does not have enough power to cycle the slide. When you get the conversion I would suggest hosing down the barrel/slide assembly with Kroil Penetrating Oil before installing it, then work the slide sever hundred times. Keep spraying down the barrel/slide assembly to wash out any residue then take it to the range. The Kroil will give plenty of luberciation and speeds the break in process, it also works great for general shooting luberication.

I have heard that the Advantage conversoin has lots of feeding issues, but I cannot confirm this personally. I also understand the Marvel Conversion will only work with one or two typs of ammo.