BillB, after asking around, my understanding is that the main difference in 1.0 or 2.0 is that the 2.0 will go to 6.0 volts, and the 1.0 will go to 5.0 volts. As far as I know, there is no way to tell from a picture, you need to click through the voltage settings to find out.
The difference in the 2.0 and 2.5 is purely cosmetic, with the Provari name being embedded into the 2.5 version, and just printed on the 2.0 version (which apparently had a tendency to rub off.)