I think there's a review at the LED museum.
Some CPF'ers absolutely love these things. I think they're a cute idea but overpriced. Their most interesting feature to (some) CPF'ers is their extremely long runtime (like months nonstop) in the low brightness mode if you use the special lithium battery. But who really cares about that? If you need that much nonstop light, maybe you want a tritium light instead of a battery powered one.
As survival lights I'd say they have several flaws: 1) lack of waterproofness; 2) lack of a lanyard hole; 3) battery and head can separate if you drop the light.
The Gerber (formerly CMG) Infinity Ultra is a nice 1AA light and yes Gerber did change the design to use a twist tail instead of a twist head. CPF'ers mostly (not unanimously) prefer the old design, maybe because that's just what they were used to. I have several of the old ones and have seen (but don't have) the new kind. The old ones do seem to have better build quality. Note that not every Gerber unit uses the new design. The first units with the Gerber logo were the old design and they switched designs a little while later.
The Ultra-G is no longer made and is in some demand on CPF, but you can buy them for $25 or so. I don't think it's really worth paying extra for the HA3 finish.
If you want a tiny survival light, go for a Photon II or Photon Freedom, maybe in the new ETS version with the yellow glop on the body. (CPF'ers hate the ETS version because the glop is ugly and peels off). The Freedoms come with a little clip that let you attach to your hat or clothing for handsfree use, a very handy thing.
If you want something a bit more solid, I'd suggest the UK 2AAA eLED, about $12 from brightguy.com. It uses two AAA's and has about 20 hours runtime and a focusing optic for a bit more reach than a bare LED would give you. It's waterproof to 1000 feet and comes with a hat clip for handsfree use.
Finally, the esteemed Arc AAA is available again,
www.arcflashlight.com is taking orders, but right now is backordered for a few weeks. They claim that orders placed today will be shipped around the end of this month, IIRC. They will supposedly bring back the Arc AA around xmas time.