It's an interesting comparison:
The Dountryman boot is about 4" wider, about the same height (but with an extra 8" depth under the flat load floor) and is about 8" shoter. So overall, about the same size, but just a different shape. Of course you could then move the rear seat forwards on the Dumpyman to create more room if needed.
The F20 is noticeably more refined than the Dumpyman. If you are looking at them then don't overlook the petrols. As the smaller petrol engines have been taken from the MINI they are picking up quite a following for being economical, refined and reasonably quick. Having driven the 116i I have to say that I was impressed. I was expecting lethargic performance, but it was plenty to keep other traffic honest, and pulled well cross the rev range, without sounding like a diesel.
Gone: Fiesta - Focus - E46 320dSE - E91 330dMSport - E82 135iMSport - R55 JCW Clubman
Now: M135i with lots of toys