I have been playing with ProM for a one evening now. The most obvious thing to say about it is that it's very small. Bearing that in mind, I was truly surprised to find out how it ground a double shot. It was relatively fast, but especially, extremely beautiful. No static, no clumping, very fluffy and the heap is nicely even and centered on the filter. Reminds me of K30, except that there's no clumping and it takes about half longer to grind. I have always thought that to produce a nice pile of fine grounds fast you need to have very large discs, but Mahlkönig seems to have done something clever here. I really expected to see some clumping and static.
There are also some things that obviously are not the way I'd like them. Most important is maybe the fact that it's hard to change beans when the hopper is full. Grinding chamber is relatively deep and there is no latch on the hopper. It is a bit shame especially because the grinder seems to retain no grounds (if you blow it empty, put in 20 g of beans, you get 19.9 g out).
The portafilter holder is not as good as in K30, but probably close enough. We'll see.
I like the overall usability. Fineness and time knobs work very well. There is only one button to control both single/double grinding and start/pause/continue and only one LED light providing feedback, so operating the grinder was a bit confusing at first. As a hint, it is important to notice that the light has a normal mode and two different kinds of flashing modes.

It works probably well in home use, but might prove a bit clumsy on a cafe where both singles and doubles are ground at fast pace.