Okay Longstreet. You're pretty new.
A Kroll is a >momentary - on - off< switch with threads that fit the ned of minim*gs, Streamlight JRs, TT3AA etc.
It has a "Tactical" momentary position, push harder to click it on, again click to be off.
The Twin Tasks major nit pick is having to cycle through the modes ie: through the LEDs to get to Xenon, or through the Xenon to get off.
The Kroll in the ends of my 1L 2L and 3AAA Twin Tasks allow me to leave them in the most usefull mode (LEDs) and I often don't even click through to the Xenon in a given use.
Krolls are an EXCELLENT addition to any light that can use them!
For a 1L or 2L TT to use one, it must be drilled and tapped to minim*g threads (I think it's 5/8ths by 17 but DO NOT quote me on that!). Do a search for member BradN. He is who did my Tailcaps here in Houston.