I briefly considered the A2, and bought something sort of similar, the Streamlight Twin Task L2, which also uses a xenon bulb for "high" and three LEDs around it for "low", and is supposed to be comparable.

I don't find it so- it's high is nowhere near my L4 high and it's is very dim next to the L4 low. After receiving the L4, I pretty well decided that I had bought my last incandescent. There may be some things that LEDs don't do as well, but this will certainly hold me until they do- which I don't think will be long. Maybe the A2 is more impressive, not sure... but I'll be the low is REALLY low. They sell it with colored LEDs for pilots to preserve their night vision, so you know it's designed for reading charts in the dark, not lighting up rooms.

For me, the short life and fragility of the bulbs (especially if the light is dropped while on) is just a killer for emergency use, now that we have tech that doesn't do that. I also don't find the tint more "natural", it just looks really orange-yellow next to the L4 (and now the Q-III) with artifacts from the filament (shadows) that the LEDs don't have.

But that's a very personal thing.

As for the U2, I was excited when I first heard about it, but disappointed when I actually saw a picture of a late prototype:

(third one down)

(there are other pictures of this prototype, and one other, in threads on candlepower).

It's just too big (not pocketable IMHO), too expensive ($270), and more complicated than it needs to be (you really need 10 levels?). I think it may be a step in the wrong direction.

Again, I think my 2-stage L4 will do me just fine until something a LOT better comes along.

I just received the Nuwai Q-IIIs last night, and this will almost certainly be my backup light. It uses the same CR123 cells as the L4 (albeit one at a time), is almost in the same ballpark as far as brightness (at least 3/4 as bright), and is about half the size of an AA Mini-maglite, small enough to ride next to a cell phone on my belt and go completely unnoticed. Nice beam too, and not very expensive. These two, the L4 with 2-stage and the Nuwaii Q-III, will be my commute carry for some time to come.