In my experience as an Appleseed Shoot Boss, I have seen way too many extractors break on them to ever consider buying one. I think a dedicated .22 AR-15 upper is a much better way to go.
The only 'negative' thing I have heard mentioned about them is that most people I've talked to wouldn't call them 'accurate' compared to other semiauto .22 rifles in their collection. I'm not sure how to quantify that, so YMMV.