Overall, looks like a pretty nice light. I kind of doubt I'll be owning one anytime soon (read: anytime soon after they're released), but looks nice nevertheless.
What I like is that it adds an option in the SureFire line that has smooth, sleek lines without much to catch or wear on clothes. Also, the output and runtimes are about perfect, especially for a 1-cell light. Add the black HA and good clip design (both bezel-up and bezel-down... why did no one, or at least I, never think of that before...), and it shapes up pretty well.
What I don't care for, however, is the tail switch. I do generally prefer clickies over twisties, all other things equal. And I guess it's cool that SureFire is now offering a 2-stage clicky. But what I've always liked about SureFire is that they have some of the best, no-nonsense, simple-as-can-be switching mechanisms. Other lights have been cool with all their modes and levels and such, but the beauty of a SureFire (to me) is that you just press it, and it goes on, exactly as you would expect it to, without having to put any thought into it. When using a flashlight, I don't want to have to explicitly call from memory every time exactly what I need to do to get another mode, or how long I need to wait before I can get back to the first mode again. I suppose I may be exaggerating this point a bit, but the Backup nevertheless seems to approach the realm of over-complicated multimode UI's.
And I must say, my immediate impression of the price was quite the opposite of the comment above. I was actually somewhat suprised at how INexpensive it is. I mean, the other lights in the SF line that come close in functionality and form to this one are the L1 and E1L, which are $135 and $99, respectively. Now, given that the Backup has a fairly powerful LED in it, and that it has 2 levels of output, I would expect the light to at least be around the $135 mark. Add to that the fact that they have a new, 2-stage, clicky tailcap, and I was expecting even a touch more expensive than the L1. But I digress...
Bottom line, it looks nice, with great form factor and perfect levels of brightness (would love to know whether the beam is designed more for flood or throw), but the switching mechanism is disappointing in its complexity (even if it is a lot simpler than most multi-mode lights out there). My hope, therefore, is that SureFire will offer a simple, twisty alternative, such as the A2/L1/L2 switch.
One last note... Is it just me, or does this light have no lock-out possibility for the tail cap?