I found the Olfa ergonomic cutter very hard on my wrist. I got a Martelli cutter, and gave the Olfa away. For carpal tunnel it definitely gets my recommendation.
One caution with the Martelli cutter - you do have to hold it "correctly" for it to work. This means extending your index finger along the back, and holding the handle with the other three fingers. If you try to wrap all four fingers around the handle (like pushing a shopping cart) you won't have any control.