I definitely need the ring - I use the light with a pistol and the T1 just doesn't quite work for that. I'm amazed and impressed that they've already responded to user input and upgraded their design.
Well, there's more differences than that, such as a more exposed tail switch, which is important for those wanting to use the rogers style grip. Also the shiney SS bezel has been replaced with a olive HA aluminum bezel. The huge clip that gets in the way of changing modes is gone. The beam appears smoother and improved on the TK10. They are subtle changes, but they make a big difference for people who need a tactical light.