I took a closer look at the site. He has a video of it milling wood. I expect it would also mill brass and aluminum but maybe sort of on the slow side.
It does look like a nice setup. I like the feature to find the tool length. I wonder if his software is open source.
Regarding the remote IO station. It is what it is. You could spend time and develop a program to run steppers with it, but a solution like you pointed to would be way easier.
In general I would not find it very useful. If you can program a micro controller I would think that you can do everything this thing does. But I did not spend much time looking at it.