Mike,
We have a Pure Oasis DAB (waterproof - so good for caravanning and outside use).
Sound quality is good for DAB - which isn't saying much - the old compression software and limited broadcast bandwidth means that it's never going to be HiFi.
I judge DAB broadcasts to be midway between FM and MW, so if you like listening to talk, sport and similar programs it's fine, but if you like Radio 3 live music broadcasts - then you will find it wanting. The JVC micro HiFi (FM radio / CD) fitted in our Eriba easily outperforms DAB on music.
Like Digital TV (FreeView or satellite equivalent) you need a good signal to get the best performance - and inside a caravan (metal box) running off the radio aerial is not the best start - an external aerial is significantly better (try the caravan FM aerial or fit a car FM aerial and only pull it out half-way (DAB broadcasts on 200 MHz, FM on 100 MHz - so a shorter aerial is needed).
Reception is some parts of the country is patchy, but generally OK - but take a look at the coverage maps already referenced.
Robert