I have both the Yukon and Gemini.
Gemini has 2 LEDs (my older one has only 1), and Yukon has 3 LEDs. Yukon's LEDs are very bright (I think the reflector helps) and a bit blue. Beam is not entirely smooth due to reflections off faceted reflector, but is not bad either.
Stock bulb on Gemini is weak, but you can replace it with a Yukon bulb (fits right in). So let's compare reflectors on both with Yukon bulbs:
The Yukon incandescent completely blows away the Gemini for throw, if that's what you want. Widen it (it's focusable) and it's not very smooth. At tightest focus it is poor for looking through the woods (too tight). Gemini is extremely smooth and wide (really an excellent beam profile), but lacks throw. It's an excellent reflector to use in conjunction with a long throw torch for occasional spotting.
Construction on both is very good. Neither is entirely waterproof (I've tested this myself). Gemini is lighter, with smaller battery compartment, but larger head. The bezel on the Yukon is heavy and protudes out a little too far, but isn't a major problem. I prefer Gemini pivot screw, as it's more rugged and can be tightened with a thumbnail.
Take the best of both and you'd have a super headlamp. Either one is very good, though, and I recommend them both.