The TA series (TA20, TA21, and TA30) from Fenix is an alternative to the JETBeam Raptor selector ring system. Unlike the smooth action of the JETBeam lights, the TA series has a more tactile feel, with a solid click at each level.
The TA20 has three brightnesses and one strobe setting, running off of two CR123 batteries. The TA30 is a very similar light with the same settings, except it runs off of three CR123 batteries that give you about 50% increased runtime. The TA21 steps up the levels, giving you nine brightnesses and three flashing modes off of two CR123 batteries.
Here’s a video that will give you a better idea: