I believe its just the thought of being able to have 2 guns in only a package that's 1 and 1/2. As for the time factor, I dont think that's what they're really getting at unless its for marketability. I think its more of the fact that its easier to do with the ACR than the XCR (supposedly).
The whole thing reminds me of the competition for making magnum auto-loading pistols in the 1980 and early 1990s. Coonan and LAR tried the whole bit with 357mags and 44mag auto-loading handguns but were beat out by Magnum Research and their Desert Eagle. Why? Not really sure, could all boil down to advertising.
Either way, I'm sure both of them are nice to have, but IMHO I'd rather have the ACR because of the reliability of the companies involved.
I'm already surrounded by half-dead brainless people already, the zombie apocalypse would just give me a reason to be productive and get rid of them.