I've had great luck with my dedicated CMMG .22 upper. Same guts as the conversion kit, but with a barrel twisted for .22LR. very accurate and no reliability issues
+1
That's really the only way to go, if you want to get any kind of good accuracy. 3" groups may work for some people, but not me. I'd invest in the complete upper. I say this after witnessing what guys at my club have went through with their conversion kits... The best example and most recent was at one of our golf ball shoots. Guy couldn't even hit the golf balls at 50 yards with his.