Don't know much about them as I've never even heard of them. But I Googled it and it appears to be line level inputs only so no mic preamps. And it's unbalanced.
Not a lot of use in most set ups. Perhaps if you have a bunch of different keyboards and synths, you could use it to route them and avoid a lot of re-patching but other than that sort of thing, you can't do much with it.
I can't comment on the build or audio quality--never seen or used one.
If they're line level like a keyboard, yes, but not mics. And,,as you say, it'll be pre mixed into two tracks, severely limiting flexibility while mixing.