I have had both long and short. Couldn't stand the short one!! It worked just fine for all the painful moves (which are really what I have it for) but my favorite thing to do with the long one is to lay on it so my spine is on the length of the roller and then stretch out my chest by spreading my arms. You can do the same thing on a ball but my head falls backwards and that is uncomfortable for me as it makes me woozy. On the roller, my head is supported much better.
You can also do some back/shoulder stretches with the longer one that don't work as well with a shorter one.
I got mine from a running store (RRS) and my chiropractor has them too. I'd make a couple calls to physical therapy and chiropractic places near you if you don't want to pay S&H.