Composition media is a similar unit but without navigation. You can still use navigation on your phone via Carplay or Android Auto.
Its kinda like RCD510 compared to RNS510.
I have never seen an RCD330G so I can't offer much in the way of commentary. They seem to be a cheap and cheerful way to get access to Carplay/Android Auto if you get the correct unit.
5C0035680B is non-DAB Discover Media.
5C0035680C/E are DAB capable units.

The OEM units support external amps properly just by changing coding and adaptation whereas the RCD330 needs a line out converter as far as I am aware.
Component protection and feature activation are the tricky parts.