Well, feast or famine to a point. Isopods will eat lots of stuff -- leaves, hardscape (this isn't good unless you want your wood pieces sanded down), bits out of some substrates probably. But their reproductive cycles are pretty slow, at least compared to springtails which can go from standby to overwhelming in a week or two with good conditions and food supply.
Yeah, the disposal issues are a problem, and regulations regarding isopods aren't widely followed. Many online isopod sellers aren't properly permitted to ship across state lines, which isn't cool. The "bug" (insects and arthropods) side of the exotics hobby is almost certainly the one that violates the most laws (USDA regulations, which are covered by Lacey) regarding possession, transport and "importation".