It was a beta version of the light, but I don't think anything changed before they went into full production. I don't think there have been any changes since then either.
I like the Novatac lights, but as someone who fiddles I found myself constantly reprogramming the modes. While that's nice, I actually prefer a light that's more simple. The T is probably what I would personally buy, because the reason I started carrying a light is for tactical purposes, but the E model would be better for general purpose.
They're actually all the same light, just with different settings programmed into them and different switches. The P model makes it much easier to get into programming mode, while you have to click the switch something like 100 times to get into programming mode on the other lights.