And the reason I decided to do the clamp on version instead of the desktop mount version is for a couple of reasons ...
The first reason is that initially the idea was that I would clamp these to my chair arms directly and have a "mad hacker" type chair, which I've always wanted. Unfortunately it didn't work out well in my setup -- for fault of the gear, I just couldn't keep them attached to my chair and still get in close enough to the touch screen for my comfort level.
Secondly, and this was always the backup plan, is that I could clamp them to the fronts of my desk and have a full 360 range from there -- they could go out more forward than the front of the desk or go back -- they are currently in the back position. I also wanted to make sure they were very stable and clamp ons don't move at all. Also they don't take up any desk footprint. You can (barely) see that on the right hand one I actually have my mouse under the keyboard. it also keeps the desk top (the real one, not the virtual one) clean and usable underneath.
I couldn't be happier with the setup.