Rob, I would go for this if I were you. Assuming the functionality is on a par with the factory fit, you won't regret it.
DAB coverage is good for me - up and down M6 & M1 but mainly in Lancashire & Cumbria & up to Scotland.
There is a 5 second dead spot just off J36 M6 on the Kendal bypass. The only downside I've noticed.
However, I used to totally lose FM signal going through the hills when driving to Scotland (in every car I have had for years). With DAB it doesn't give a kick, so much better.
If you listen to stations like Talksport or 5live(?) it is just faultless on DAB. None of that horrid white noise.
Just do it mate.
August 2012 F10 520d SE sport automatic, Jet Black, Oyster\Black Leather, light ash wood trim, Professional media/ navigation, mobile apps, Internet, DAB radio.