When I bought my car in 2014 the full DAB radio hadn't come out , so they fitted this thing with a tinfoil arial stuck to the ns windscreen and gave you a black plastic thing with 4 segments and a centre knob working by bluetooth.
They claimed you could program it for 12 presets, but it was not compatible with the steering wheel mounted program changer. A lot of fiddling about to program and to change programs whilst driving.
In the end I asked them to take it out and refund all I had paid, which they did reluctantly.
Now that Mazda has brought out an integrated DAB radio , I believe all they do is change the head unit, though I am not sure about the extra arial required.
Yours being an estate car and fitted with a sharks tooth arial, they might just be able to adapt that painlessly.
When you think about it , radios now are just a small printed circuit board assembled by cheap labour and machine soldered, made by the thousand but dealers stick it to you.
I hardly use my radio at all in the car, just have the memory stick playing on Songs ( which play alphabetically by song title so on shuffle by default, no fiddling with controls etc) and when away from home the TA is turned on.
Are you aware of the warranty upgrade to the bluetooth module (you have to ask for it) such that the mp3 player does not start at the first song each time you start the car, rather than carry on were you left off.