as described in this thread, i returned my gtl 21 for warranty replacement. they sent me a gtl 22 instead. the gtl 21 has a momentary switch like the m3/m6. pressing down all the way locks the switch in the "on" position. the gtl 22 differs in that brief press of the switch turns the unit on, and another brief press turns the unit off - like a push-button switch. a sustained press will cause the unit to gradually brighten. releasing the switch stops the brightening at the desired level. this is explained in the literature as a "dimmer" feature- a little misleading. the system is more useful than it had previously been described to me. a further sustained press will continue to brighten the unit, and a short press will shut the unit off. to go immediately from a dimmed light to full blast- two rapid short presses. the laser feature does not dim (or brighten). when laser only is selected, a press of the switch for any duration simply turns the laser on. another press to turn it off. when light and laser are selected, and the dimmer (brightener) feature is used- the light alone will gradually brighten. when you release the switch the laser comes on. so you can see- the gtl 22 combines the advantages of the m6 AND the m6 led. and then some. when i first removed the unit from the box, i thought it was a defective gtl 21. after looking at the model number, and playing with it for a few hours... i'm impressed. the controls become instinctive. a lot of bang for the buck. unfortunately the fit issue, the hard to grasp latch, and the robustness of the little bearing pips to focus the beam- still need to be addressed (imho). to me these are now minor problems compared to the value and versitility of the unit. ymmv. -eta: another small glitch that must be true of all the glock lights: a tug or press on the bezel (such as can happen holstering and unholstering) will change the focus of the beam slightly. imho glock needs to rethink the use of cam slots to focus the beam in favor of a more conventional thread.