Just got my L2T hosts in today along with a 4.2V, single mode XML Solarforce dropin. This would not be safe for use on 2xCR123 cells, but it's pretty dang impressive on a single 18650 which will also provide longer runtime than would two primary CR123s. I specifically wanted a single mode drop-in for this light, but I also have a 5 mode, 6V XML Solarforce that is great. I'm just not crazy about the flashy modes. Comparing my two Solarforce modules, the 5 mode module on Max mode on two fresh CR123s doesn't seem to be quite as bright as the single mode on the 18650, but they are close enough that you'd never know the difference unless you were comparing them back to back.
My current take is this: if you want a single mode module and can live with using 18650s rather than primary CR123s, I can highly recommend the Solarforce. If you don't mind the flash strobe/SOS modes, I can recommend that Solarforce. If you want three modes (high, medium, low) and no flashy modes, the Thrunite XML or one of Nailbenders modules would be my suggestion. I could easily live with any of them, personally.