lol, i see you're getting into the spirit of flashaholic-ism, first the NDI now lookin at Jetbeams eh? Also, there is another model you left out, the RRT-1 (which is more a thrower light than the RRT-2)
the RRT-0 is smaller than the RRT-2. Both of these lights utilise a control ring which allows you to choose between a few fixed output levels.
The Jet III M has basically 2 modes, max when the head is tightened, loosen it for the 2nd mode which is programmable using Jetbeam's IBS (Infinite Brightness Setting) user interface.
A more general use light would be the Jetbeam Jet III Pro ST (Broad Voltage), it has 3 individually programmable modes and is very handy and pocketable. The BVC means that the light can run on either 1x18650 (3.7v) cell or 2xCR123(6v)/RCR123s(7.4v).
You're right, 18650s and RCR123s are rechargeable cells, a lot of CPF-ers use 18650 cells as they have a very decent runtime and convenience of using 1 cell instead of stacking 2.
AW (can be found on dealer's corner at CPF marketplace) sells the cells and chargers too.
I own the Jet III Pro ST but none of the others. I also own the M1X, the interface is the same as the Jet III M which is pretty useful if you only need 2 modes and ready access to max.
It boils down again to what you need the light to do, i like my Jet III Pro ST as i can program it according to what i want. Sometimes i want the first click to give me max, other times, i want it to come on in minimum, and then again sometimes i need it to come on in strobe first etc etc etc. That is the advantage that the Jet III has, 3 modes, individually programmable.
Happy hunting (again)
Oh, and i may just say, good calls on getting quality lights instead of going the route i went, getting cheaper lights first and getting frustrated.