DAB radio is brilliant - if for no other reason than you can get BBC7! OK, my choice of stations might not match yours but if you listen to a lot of radio then you really ought to be looking at getting DAB.
Reception is generally very good (better than VHF-FM). Sound quality will depend on the brand that you buy. (As with any radios, the cheaper sets usually have poorer quality speakers. Look for well-known brands like Roberts and Sony).
Just a few words of advice, however, regarding your question "Is it totally portable?":
1. The full range of DAB stations is still not available in all areas. Use the postcode checker at
http://www.bbc.co.uk/digitalradio/ to find out what you can receive in your area.
2. We've got used to the idea that almost anything can be 'miniaturised' down to incredibly small sizes. At the moment, however, portable DAB radios are usually still quite bulky things when compared to CD players or MP3 players.
3. If you're hoping to use a DAB radio while 'out and about' you need to be aware that battery consumption on most current models is much higher than you would find on a conventional, analogue radio.
Hoping this helps,
Chris