I'm looking at them to. I keep going back and forth between the gas powered models or the pneumatic Rohrer. I'd really like to hear from some folks that have used the gas powered models. I know there're some cheap off-brands on Ebay with knockoff Honda engines, but I surmise they're junk and the cheap engines will just cause frustration, not to mention that repair parts are probably non-existant. So the Titan or Skidril are probably the models to have, but pricey. I've used the Rohrer before and it worked well, albeit a little clunky. Plus, I'd need to have my welder/generator to run my air compressor to run the Rohrer.
You could just bite the bullet and get one of these
Propane Hammer 
Portability and simplicity