Gamaras, amphipods and ghost shrimp...a down side, or not?

Found a site that sells cultures of fish-friendly food and creatures...Wondering if anybody has experience with scuds, (gamaras), amphipods and ghost shrimp...the site guy said that they clean up the substrate, some inhabit the filter and are generally good, clean live food for the angels, dithers, corys, etc.

Does anyone have an opinion on this?...It certainly sounds sound...Ken