I have been using the TypeMatrix keyboard for over 3 years now and it was a great experience. I feel much better in my left hand than before (my right hand is still a bit torturous due to the mouse). In fact, the learning experience at Dvorak was especially interesting, as you can feel how the brain is rebuilding and how your mental keyboard model is evolving.
Since the Typematrix keyboard paves the Dvorak at the device level, I found it particularly effective to configure the keyboard in the operating system as US-International, allowing me to type in almost any accent. À, ë, Ö, everything is much simpler.
I think the skin is pretty good, softening the touch, and the keyboard is much easier to clean. I did not feel it slowing me down.
A word of advice, though: if you intend to go all the way Dvorak, it will take some time (from 1 to 2 months) to return at full speed. And on other computers, or on laptops, it becomes much more difficult to enter data. I actually bought two keyboards, one for home and one for work, and it works very well, since I rarely have to type anything else, but for other applications this can become more problematic.