I have had good experiences with MDL for livestock. The specimens that arrive have all been of great quality, size and coloration (as if I had gone to an LFS and picked them out myself). I have purchased corals, fish and inverts from them. Except for the UPS issue mentioned below, I have not lost any livestock that I bought from them (all still alive and well)
The only time I ever had problems was with UPS, and not MDL, but MDL still went above and beyond to make it right.