I've found DAB terrible in every car i've used it in. Cuts in and out, doing the radio equilavent of the blockiness/stuttering you get on Freeview. Would often be in mono or some awful bitrate, and at its best it sounded the same as good FM reception.
The only benefit is the additional stations IME. For everything else FM is far more suited to in-car listening.
Driving down the M6 I had a more consistent 3G signal for online radio streaming than I did DAB.
Although some people report it's fine so either the implementaiton varies massively between manufactuers, they drive solely in a high signal strength areas, or lies.