I have both a dedicated upper and a conversion bolt. I have no problems with either. If you want tight groups, go with a dedicated upper. If you're just wanting to cheaply plink with your 'real' AR, then go for the bolt. My conversion bolt can hit clay targets out to 100 yards using a 3x magnifier. That's good enough for my needs.

As for cleaning after using the conversion bolt, I generally do barrel-only cleaning at the range after shooting 22 and then fire a few rounds of 5.56 to clear any gunk out of the gas system. I do a thorough cleaning at the house to get all the grit out of the chamber and lower.