I bought a frogpad lefty and put some serious time on it when I was forced to do some diagramming and other mouse-driven torture. It was better than moving my right hand on-and-off the keyboard and mouse. If I could get Cherry Browns or Topres on one, I'd probably stick with it. but it has the old, flat, chicklet keys that make me sad.
But, I've gone back to emacs and my two-handed Realforces and Leopolds, and stay off the mouse by using procedural graphics with Tikz and Graphviz and Dot as much as humanly possible. I'll probably never leave that world.