The Martelli rotary cutter is ergonomically more correct and therefore puts much less stress on the hand and wrist. I have one and I have to agree it's easier on the hand and wrist. However, it does take some time to adapt to the different hand position. I also (if I am remembering correctly) found it difficult to use with the June Taylor Shape Cut mat for cutting strips.
Aside from the Martelli rotary cutter, you might want to consider investing in an Accuquilt Go! or Accuquilt Studio die cutter. Lots of people with arthritis find those machines easier to use. The downside is the dollar-cost.
Edit: Here is a link to the rotary cutter portion of the Martelli website:
http://www.martellicatalog.com/mm5/m...tegory_Code=RC
They also have quite a few videos on Youtube. Here is a link to their Youtube video about the cutter:
http://www.youtube.com/watch?v=QJRQGFYoO2Q
Note that their cutters come in a right-hand and left-hand version. You need to order the correct one for your handedness.