It's actually quite a good looking aircraft, with shades of Flash Gordon's War Rocket Ajax in its appearance (google it). The flexing of the wings on landing was impressive, and makes you wonder at what point the engine pods would come off.
The question I have is with regard to later Pegasus variants, which could have substituted the RB162 batteries and turned the Do 31 into a four Pegasus design, making it even more useful by not having to cart around the batteries when they were not doing anything useful. Four Mk.103s would have given over 80,000lb of thrust, as opposed to the Pegasus 5/RB162 combination as used, which gave a combined 66,000lb.