I'm wanting a .22lr AR for a few reasons.  

First off, I like shooting ARs (ergonomically) and also enjoy shooting 22s (economically.)  Why not combine the two?

Secondly, I have a very young son, and am forward-thinking about taking him shooting.  After the basic single-shot 22 rifle, I hope to quickly transition to shooting ARs (in 22lr), to teach him familiarity with a "real" rifle.  This would teach him to use the peep sights,  get comfortable with handling the AR in shooting positions, and learn the operating layout of the AR rifle.

Thirdly, I want to shoot squirrels, rabbits and other small game with a .22lr instead of a 5.56NATO.

SO, would you think the Ciener conversion kit would work well in this role, or do you think I should go for a dedicated upper?  I'm thinking the Ciener would work JUST fine, even though it won't be AS accurate as a dedicated upper.  I'm not going for a taret gun, but a plinker.  Does the Ciener shoot Minute Of Squirrel at 25 yards?

ETA- I've got three ARs now, but would probably get a Rock River midlength as a "host gun" for the Ciener kit.  If I got a dedicated upper, I'd get a lower for it.

JW,
i have two Ciener kits, for what ever reason i can not explain, one will shoot 1/2" groups at 25 yds., the other shoots abt. 1 1/2" at 25 yds. IN THE SAME SP-1 !! but at 75 yds. there seems to be no difference with 3" groups.

i believe you would do well to get a dedicated upper.., which is my next buy from Bushmaster, in that respect, you can head shot every squirrel at 75 yds if you want.