They work pretty well, and if they weren't so expensive I'd probably buy more of them.
You can shoot them quite a lot, especially with .22, but as people have said, if you shoot the frame, it will break or if you hit up at the top, it will be unable to spin. I have broken at least two of them over the last year and a half.
I picked out a few .22 bullets that got stuck at the top against the metal, and was able to keep using the target, but they do get worn out. A hit on the frame with .223 will break cut the metal clean off of course. If you are unlucky and hit the thin part that hangs the little spinners down with a lot of .22, you will eventually break the target off.
Still, they are a lot of fun for my kids, way better than paper targets for immediate feedback, and a lot easier, and ultimately not any more expensive, than running up and putting clays on the berm. The cheap $20 one doesn't cost any more than the steel spinners, and lasts about as long under fire.
I just ordered the ball they sell. At $65, it's way way expensive, but we have a lot of fun shooting plastic bottles with .22's , and I want to try something to shoot with .223 that would react. I have been keeping my eyes open for some surplus plastic objects which might make good reactive targets, but so far haven't found anything which will stand up to rifle fire for long, and I don't want to leave plastic bits all over our nice clean range.