Wait a second, isn't the guy from FOB in their music video and sings background vocals on that song and quite a few others on their latest album? I'm not saying, I'm just saying.
yeah, one of the guys in falloutboy is childhood friends with the singer from gym class heroes. he hooked them up with a record deal.
as far as their sounds, its nothing alike. gym class heroes has more in common with the roots than fallout boy (although admittedly, the roots are a lot better)
give gym class heroes a shot, ive seen them live twice and they put on a pretty good show. plus, the singer is a real cool guy, who talked to me for about an hour outside of the venue. we talked about rare adidas, graffiti, and hall and oates. it was pretty cool.