The 'clean' summation is for headroom, which is a huge plus come mix time. It's also for integrating outboard gear or for simply summing 4 stereo stems to a mix buss chain. This is a very handy feature not to be overlooked.
The summing portion is also brilliant because you can wire in your analog gear and use the D-Box to monitor at different points in the chain, which is a great way to evaluate your gear.
The summing portion is so much more than simply summing on this box. I'd argue it's more for utility, headroom and properly wiring up your analog pieces. It's certainly not a character piece unless you add to it...
If you don't plan on using the summing portion of this box, I'd simply purchase a Dangerous Source and save a few bucks.
Lastly, I'm a biased D-Box owner
I just love this thing. It gets used at all points in the chain for me - from tracking to mixing!