I got to play with my Gerber IU more during the weekend and really like it. The beam is a bit blue in the center and more greenish as it goes outward, very similar to the tint and color distribution on my CS-modded KeyMate. I'm not sure if the new IUs run CS's already or not, but it's output is very close to my CS-KeyMate which is quite bright (not as bright overall and less intense hotspot, but close in overall output when I was testing them in my dark bathroom). Seeing as the IU runs a boost converter up to the LED's VF (3.6V typical) while my KeyMate is DD off 6V, the new IUs may actually be running CSs (or I just got a really bright one?). Also, my KeyMate uses a reflector which may account for the slight amount of a overall output (reflector being able to collect the small amount of light which may be loss with the IU's no-reflector design).
I too would like to know how to open the head. I tried on Saturday with a couple of strap wrenches with no success (the finish survived much better than I expected from my removing the clip). I can likely swap the LED afterwards (unless it's an unusual process), but I just can't get the head open. I question tho if swapping in a CS would increase brightness that much as I've stated above, the overall output is close to my KeyMate which overdrives the CS at 6V (or close to that).
I liked my Gerber IU so much that I went to pick up another one for my fiance on Sunday (tho, I don't think she'll use it much, so it's really just an excuse for me to pick up another one...haha).
Regarding a comparison to the new X1, I don't have one. I was looking to pick one up, but was initially held back mostly due to the price (again, hard for me to justify a 5mm LED light for $20) but still really considered it because it was from Inova. However, after reading the reviews on CPF about the QC issues with the glued in lens (which isn't a bad method IMO, but they need better QC) and switch, combined with the price I already had difficulty justifying, I decided I won't be purchasing one at all. While standing at the flashlight isle at Target, it's hard for me to justify the X1 for $19.99 when I turn my head 10degrees and see the Dorcy Super 1W for $19.99 (tho, I don't have a Dorcy 1W either).
ACMarina - I definitely like what I've read that the original CMGs were built like tanks, but again, I'm not very fond of the exterior design. I know many people will say they don't buy lights for appearance, but if you have more than 1 or 2 lights, it's not for necessity anymore and becomes a collection/hobby in which case for me, appearance/aesthetics does matter then. I know many others like the CMG design tho. Again, it's just my personal taste.
Allnew2me - the IU isn't unregulated. I know many CPFers call lights with voltage regulators "semi-regulated" which isn't completely true. It depends on how you define regulation and what you're regulating. Most CPFers define regulation as current regulation, in which case, "semi-regulated" is a decent description. However, a voltage regulator, even a simple buck or boost converter, is still a regulator.
Goatee - As others have mentioned, a polished reflector seems to help a bit. The reason some companies don't use them is mainly (I believe) because 5mm LEDs already have a built-in optic (the big high dome) that focuses most of the light. I'm sure light is lost from the sides and angles not hitting the optic (that's why you see light when you look at the side of the 5mm LED) so a reflector should help to recollect some of this lost light.
Oh, and runtime isn't sacrificed when running the CS because the CS draws the same amount of current and runs at the same voltage as the standard LED, but produces more light. It's simply a more efficient LED. Runtime is affected by how much power is required by the LED/load. Since the power required is the same, the runtime will be the same while producing more light.
paulr - I knew online vendors that sold IUs for $15 or so (seen down to $14.xx, close to $15), but as I mentioned, considering shipping, it's close to $20 shipped. The IU at REI was $16.23 OTD with tax included...cheaper than any online retailer and making it more justifiable for me.
eebowler - I haven't had a chance to test runtime yet. I ran my Xnova8 for about 35hrs straight still producing light off an AA cell that read 1.36V open voltage. I say "about" because it died in the middle of night while I was sleeping, so I'm not exactly sure when it died. It definitely lasted over 30hrs (still enough light to navigate a dark room/indoors when I went to sleep). I expect the Xnova8 would've run more than 40+hrs had I used a fresh AA which typically reads 1.6-1.62V open voltage. I do plan on testing the Gerber IU on a 1.36V open voltage AA also to get a comparison. I recently modded my Xnova8 by removing all the 8 LEDs and replacing them with a single Nichia CS in the center position. I was hoping directing all the current to the single CS would result in the same brightness or brighter overall output than driving all 8 normal-5mm LEDs at only about 10mA each. It's decently bright, but still a bit dimmer than the IU now. The current draw dropped for some reason when running a single LED. I think it's due to the load impedance seen by the boost circuit being lower with multiple LEDs in parallel, so now it sees a higher load impedance and can't source as much current.