I specifically bought the desert pentagonlight because it included the red screw-on lens. Attaching the red lens is quick and easy; providing adequate map-reading light at night. Also, the included clip great as you can leave it attached to your belt or molle vest for hands free lumination. Only issue so far is that the on/off button requires a firm push to keep the light on (as opposed to just on while you're pressing the button). Not a big issue, though, just takes some getting used to.
Pros: ultra compact
Cons: on/off button not very tactile
This review was written in the old system and had content requirements that are different than reviews written today.