I've used the Putting Arc and had great success. I have had so much success that I am getting these for the kids I help during the summer. I was reping a putter and I took the Putting Arc along to help increase sales but everyone wanted the Putting Arc instead. I would reccommend the MSIII for your home use and the T3 to put in your bag. I believe they even offer a money back discount if your putting doesn't improve.
"Putting is not a mysterious art, great putting is an ARC"