I have a 2017 GLA that does not have DAB radio (poor show from Mercedes). Currently I use the absolute Radio app on my phone and stream that when in the car via the Apple car play. Seems to work quite well, apart from the odd dead spot losing the 4G signal. Stream up to 4 hours a day in the car, 3 days a week, the streaming has no hit on my bandwidth allowance whatsoever. May be an option instead of installing the DAB converter etc.
There is a RadioPlayer app that will stream most any radio station via car play if you want something different.