How do I put this carefully...
There is little or no difference between DAB receivers overall. Individual sound quality relies on cabinet materials and speaker quality but not from the DAB broadcasts themselves.
The broadcasts are little better than listening to a poor MP3 (DAB is still based on MP2!). The bitrate (quality) is very low for all stations except Radio 3 which is only just at 'CD' level.
Thats how it is. FM wont be switched off for sometime until at least 50% of listening is via DAB (NOT including the internet, satellite or freeview).
Roberts can be expensive, Pure can also be pricey but they all use the same chipset as the supermarket or Argos cheapies.
Its like choosing between 10 different cars that all use an engine from one manufacturer - some will be basic, some will have plenty of toys but overall performance will be the same.
*EDIT - dont rely on the postcode checker for coverage either. This can be very inaccurate. The radio may work in one room but not the room its intended for.
The BBC have upgraded or are upgrading transmitters since analog TV was switched off (now used by the mobile networks for '4G') and reception has got better. But, content hasnt got any better. In fact a lot of commercial stations have decided not to invest or to even pull their DAB broadcast altogether with just web based services.
Personally, I would hold on or use a wifi enabled set or just borrow/ buy a cheapy for now.
Then theres DAB+.... Used abroad but not here nor is it likely as the take up is just too low. And if they do go to DAB+, it will be another embarrassing amount of redundant electronics sent to the landfill (well, 'WEEE' anyway) to join FM radios for company.