Well, for me the quality isn’t there, for one… the characters look like potato. They just don’t come out looking like high end character meshes. Secondly the materials seem to be not so great. The last thing is that you don’t get any facility for making them in engine, which is a big benefit (e.g., for a customization system that works in game).
For spitting out a really basic prototyping character, sure. But we’re kind of talking about having a character creator mesh/system in UE4 itself, which would allow for both higher quality of the mesh/materials, as well as using the customization system in a game directly.
Kind of apples to oranges to my mind. Sure Fuse and Makehuman are options, but the quality isn’t really there out of the box and there’s no facility for using those customization tools in engine/at runtime.