I was just looking at all the bullpup shotguns recently and bought would slightly opt for the Kel-Tec KSG myself (the newer generation) (has the same round capacity of two magazine tubes). The DP-12 is made well out of the box for sure and has been getting a lot of press since last years Shot Show. Keep in mind it is 2.8lbs heavier (41% more), 3 inches longer out of the box (about same barrel length, DP12 is only 3/8" longer). Also, the pump action rhythm of one pump and pull trigger twice can screw some up; pump, shoot shoot, pump shoot shoot, etc.. You may not think this is significant and can be learned (sure for the range), but is against the grain of our natural thinking process, which usually goes out the door when we are under stress. The firing mechanism is also a little more complicated in the DP-12 and is not proven.
The DP-12 also requires to fire both shells before reloading the next shells. Or you can pull the release leaver to empty the spent shell and the unfired shell) With the KSG, you are able to load and select from both tubes at will, which is an advantage if you put specialty rounds in one tube, and another in the other tube.
The KSG has been out for 5 years and the company worked out their beginning issues and now has a reliable shotgun. The DP-12 is sure an interesting shotgun, but would not be my first choice.