I've got both the IU and the Civictor, but it's the IU I use the most.
I love the Civictor - it's thinner and weighs less and is easier in your pants pocket - but it's a bit of a toy. . . I find it's too bright for most indoors flashlight use. It just hurts my eyes when I switch it on in the middle of the night. If I was hiking in the woods I'd use something with a bit more power and longer runtime - SL PP Lux, not a single-cell light.
Yeah, the IU is a bit of an emergency light. It's kinda utilitarian. I don't get on with the rear twisty thing. It just seems wrong. But it's just the right level of light, and with a nice flood, for close tasks. And that's why I use it so much.
I keep trying to replace it, but keep coming back to it.
I also have the Dorcy 1AAA, which is just a bit brighter than the IU, but I find the beam blotchy. It's in my sock draw right now.
The IU is not a keychain light. It's too big for that. It'll go into cargo pants, I guess.
Maybe wait for a two stage Civictor to come out. . . Or for the FLR review of the Streamlight 1AA Task Light, which is supposed to have a low level equivalent to the IU and a much brighter high. This won't be a keychain light, either.