Buying one of these would be reasonable for solo mining on your laptop while your working in hopes of solving a 25 BTC block. The odds are against you, but the possibility is there. And for only $20 it's not too expensive. You won't make enough at a pool to be able to withdraw very often as the minimum is .01 btc usually.
It would make more sense to go buy a couple of lottery tickets instead. That way you know right away that you lost instead of having to wait.