I don't have one myself, but my uncle has one that I've shot alot. Some FTF's, but hey it is just for plinking with. Mags are a pain to load, but most .22's are. I don't know if they make a loader for them or not. Ideally, you should probably get an upper with an sp1 barrel for use with it.
However, I've heard that the owner rivals that of ASA for ahole of the year. If you have problems with yours, I don't think I'd expect stellar service.
All in all, a neat concept, but you could almost get a 10/22 for the price of the kit alone, not even taking into account getting another upper for it. I guess you could make the argument that using the .22 conversion kit would be better "training" for an AR, but the ballistics of the rounds are obviously so different, I'm not sure if this benefit is really there.
Rocko