The issue kayn is referring to is not necessarily the air certification (though that's part of it) but the vetting by AFRRCS. They, reportedly, only allow radios that have passed their testing plan into their "permitted radio list" and onto their system. To date, the Technisonic is the only aviation radio on the list.
Though it seems odd to me that it would need vetting if it is just an APX in a box, unless the box does something to how the APX operates. The full vetting procedure (AFAIK) is available in the AFRRCS Handbook and one would expect if the APX is vetted, that a device which uses the APX as its core would inherit that vetting.