The details are very Imperial in nature: blocky structure with techy do-dads, tipped with a strange crystal. The details are a bit crude, but well done. The casts are quite clean with little to no warping on any of the five rifles.
The guns are large when compared to other guns, and herein lies an issue. The guns are too big to fit in normal arm pairings. You have to options: either use arms with wide spacing, or as shown below...
Trim the gun down. To make it fit, I cut off the butt of the gun, and the protruding section on the underside. Whilst this dies make the gun fit, it does defeat the point of having these details. To combat this, you could have the gun held one handed or "at ease".
In terms of an in-game use they are fairly universal, as they have generic design features, with none of the defining features that Melta, Plasma or flame weapons have. I could imagine these guns being suitable for any of these. The distinction could be masks by painting the crystals different colours (green for plasma, red for flame etc.).
Overall these MDGs have plenty of potential. Whilst blocky and potentially awkward to fit, they are a nice change from the widening array of similar looking special weapons offered by many companies out these.