The X21 is interesting, and you'd probably enjoy it, but there are better options out there for a lot less money & a lot better quality. I just looked up the X21 and saw that it cost $300!! I own 4 LED Lenser lights (T7, H7, and two Police Tech Focus models), and like them ok. But, since I found better quality for about the same money or less I won't be going back to LED Lensers any time soon (& I now own over 30 lights.) Lots of folks on cpf feel this way; although I feel many are overly critical of LED Lensers. They are pretty good, but there are better lights available. The main reason I like brands like (Fenix, Thrunite, EagleTac, Olight, Quark, Zebralight, & Nitecore) better is because they produce better quality, smaller & more lightweight lights, with regulated light output, and with more output options in roughly the same price range as LED Lensers. LED Lensers are IMO mid-grade level lights for the same price as high quality lights like the lights listed below. LED Lenser has a long history of over-stating their light's output levels & runtimes. They seem to be correcting this, but I am unsure at this point if the over-exageration has ended.
So, before committing to the X21 do some research on lights like - Fenix TK60, Fenix TK41, Fenix TK50 --- All of these lights run on common D or AA batteries, and are all less than $150!! Much better quality, regulated output, and with more output options.
Another option would be to use Li-ion rechargeable batteries in lights like - Thrunite Catapult V3, or EagleTac M3C4 Triple XM-L, or Fenix TK35. The advantage with these lights is that the much more powerful Li-ion batteries makes for a much smaller & more lightweight light with incredible output & runtimes. All of these lights cost less than $150!! Each of these lights uses two 18650 Li-ion rechargeable batteries (or they could also use four CR123 non-rechargeable batteries.) The best brand of rechargeable Li-ion batteries to buy is "AW" brand with a good charger.
Go to websites like goinggear.com or fenixtactical.com or lightjunction.com or fenixlight.com to research these lights & batteries. Also, 4sevens.com has a large list of AW brand Li-ion batteries for sale plus a good charger.