a) The vast majority of satellites are "prototypes." They're built a few at a time, extensively tested, then launched. In the case of satellite frameworks like Cubesat, they're open source and tested every time someone launches one.

b) This is not untested tech, at all. Cubesats have been using consumer technology in satellites extensively, both by startups, hobbyists, and academia (doing advanced stuff like orbital reconfiguration, atmospheric sampling, telecommunications, etc). Combined with NASA's existing suppliers for aerospace grade components, these satellites which have a really high success rate.