DAB car aerials tend to come in three sorts - horrible sticky on types, expensive DAB only roof mounting and horrendously expensive combined DAB, FM and AM roof types.
I'm considering a DAB radio mainly for the BBC comedy channels, and I've got at the moment a wing mounted telescopic aerial - so not the modern built into rear window type. I've seen adaptors to allow the one aerial to feed both inputs on DAB radios but wonder whether they work even reasonably - they don't seem to be sold by the DAB radio makers.