Kelly Wheels don't crack when you drop them. :P
It's all about useer prefs. You have to get 2 Kellys. 1 for 16 and 1 for 35. The SamCine does both, and I think it's a much more visual solution, especially when you're learning.
I've had my SamCine for over 12 years, and have never owned or used a Kelly Wheel.
Pick up a Palm III on ebay and put pCam on it. Probably the cheapest alternative. And also a good visual representation of what's going on. Plus it has lots more features.