For starters, it's the most feature rich box available at the moment. Large hard drive (over 80 hours), USB connectivity with PC and Mac for transferring programmes and MP3s in both directions, and fairly straightforward to use out of the box. Picture quality is excellent, and the twin tuners mean you can watch one, record another, watch a previously recorded show while recording two things, and in some situations watch one while recording two others.
It also has a pretty active independent web forum with lots of knowledgeable and helpful users, and the UK distributor provides good service; experience with bugs so far suggests they're pretty keen to respond quickly to issues, and to listen to user feedback.
On top of that, and one of the key benefits for a lot of users, is that the box can be extended by adding third party software - so if you don't like the look of the built in EPG, for example, there are several alternatives you can try instead. Some of those provide extra features too, like searching for programmes by name.
If you're prepared to put in the effort, it's also the only DTT box so far that you can hook up to your computer and do things like automatically program recordings from DigiGuide, or download the RadioTimes EPG listings instead of the Freeview ones.
Not everyone needs that flexibility, but many do appreciate it.
There have, of course, been bugs, but not more than other twin tuner models, I think.
Nigel.