SayUncle has reviewed the Brownells’ AR-15 .22 LR Conversion Kit for Shooting Illustrated. It is well worth reading.
The bolt design, which is mostly the same across all the .22LR AR-15 kits, is ingenious. I would never have thought up that concept.
What is appealing about Brownells’ kit is that the magazines are similar in size to the AR-15 magazine. The other kits I have seen use magazines which are small and skinny.