I'm looking at an Atchisson .22 conversion kit for my DPMS.  I was talking to a LEO at the range the other day and he had one for his AR that he really liked.
Anyone out there had any experience with these?

Mine was worth every penny (and maybe a bit more.) I didn't have to fiddle with mine at all to get it to work 100% in semi or full-auto.

I love mine now that I installed a stronger spring which I bought from Compass Lake Engineering.  I use it with a dedicated 22LR upper built by KKF.  

A guy gave me a "junk" barrel which was always sticking 5.56 and I installed the conversion on this, my "dedicated" .22. With the right ammo,(cci- mm) it will always shoot under 1/2" at 50 yds. I used it in my SP1 for a while and it took me all afternoon to clean the barrel. With the dedicated upper, the more I shoot it, the better it gets. I think this is true with all .22's. Never clean a .22lr. They have a wax build-up which is normal, and seals the barrel. I'm not talking about match shooters! I know you guys clean just like we clean .308's.  Good shooting.
Al

Had my Atchisson .22 conversion kit for about 6 years now... Work great...