First some notes: I'm not posting a full review, since I just got it and won't have the time to build a converter for a while. Also, I don't have a camera, so I'll just use a picture that I found.
Borrowed from: http://www.asl.dsl.pipex.com/symbolics/photos/IO/index.htmlConstruction, size and weight:It is almost identical in size to the Model M mini: just a few millimeters larger in width and length. Very similar height and vertical profile. I think that the entire case is metal. I weighed it at 4.8 pounds, compared to 4.0 for my mini. It feels very solid and well-built.
Key feel:I'm not an expert on the different types of switches, so I don't know exactly how to classify it. There is no tactile bump. It requires enough force to move that I wouldn't expect any accidental key presses, but once it starts to move, there is almost no resistance. There is no mushy feeling, though. It has a very shallow throw.
The keys themselves have an interesting shape. They are noticeably slope down, instead of the slope coming from the way that the rows are mounted. It doesn't really cause a difference in how it feels, though.
I can't give an opinion until I can convert it and give it a proper testing, but if I like it, then I am excited about being able to use Emacs with this, as well as creating all sorts of macros. Most of the keys that are missing can be reassigned to what's available. For example, the right-hand set of Symbol, Meta, Super and Hyper are the same layout as the arrow keys; the Symbol key is wider, but its alignment still feels just like the arrows. It will be trivial to reassign the symbols to match my preference.