What are the odds that he could solve a block with his USB miners? Thinking in terms of time, how long would it take to get a 25BTC block reward? (That's how that works, right? Newbie, here:-)
1 month, 1 year, 100 years, 1000, years?
As I understand it, it is a bit of luck too, right? A bit like gambling?
When you are in a pool it will allocate the easiest shares to the slowest miners. He doesn't have to solo mine. Meaning he will get payouts even if they are really really tiny.
Also, not everyone buys these little USB's for profit. I bought one for my younger cousin just to get him interested. Didn't care if it would ROI.