IIt's a good quality radio in the MINI. I have the same car and the same DAB radio. I spend most of my driving time in and around London and the home counties. Coverage is as good as I got on the FM radio in my old car. Of course, if you're tuned into the Essex multiplex and you drive to Hampshire you will lose the signal. That's no different to FM.
What I like about DAB is the enhanced choice. FM (with a few exceptions) seems to be filled with the same 10 commercial stations no matter where you are. The same playlists, the same message and even the same jingles in a lot of cases. DAB has a lot more smaller stations available and gives me access to a much wider range of music.
In my opinion DAB is not as good as FM - it's better.