A simple switch may have been optimal when the $$ difference between an intercom and audio panel was thousands of dollars, but now that it's literally single hundreds of dollars (sometimes even less if you scrounge), there just is no strongly credible argument
NOT to use an audio panel. If you're using two radios, it means that you likely have at a minimum $10K of goodies in your panel. Why mess around with a sub-optimal (yet I concede it
will work) solution? Gil's point USED to be valid, but there haven't been ADF or DME switches on experimental audio panels for many years now. Instead they've been optimized for what experimental builders want - things like multiple radio controls, multiple alert inputs, configurable alerts, switches for managing aux feeds, extremely strong music management, phone call management, crew/passenger management between pilots/passengers, bluetooth connectivity, USB interface/charging (PSE), etc..
Being stubborn, a Luddite, or proving a point that you CAN do it that way doesn't count!
Cheers,
Stein