They breed like flies. They breed so prolificly that I had my babies breeding in the growout tank when they were barely old enough to sex.
The street value on these fish is just a couple of dollars retail, maybe 50 cents trade in each at the LFS (if they even want 'em). That said, I had no problem using the offspring as live food for more important fish.
Whoever told you that guppies are the only ones that would breed is either pulling your leg or completely clueless.