People routinely clamor for ridiculously-thick phones already so they can get huge batteries. I don't think the size (effectively two phones) is a big deal; I already carry 2 phones in my pocket pretty routinely with no problems.

This folding phone seems targeted at letting people carry a phone with a gigantic screen. People that are buying XL versions of existing phones (a surprising number of people) that want even bigger screens (that still fit in the pocket) seem to be the target, and/or people who want a 2-in-1 phone+tablet.

I don't really like large phones, but I do like using tablets. Having the choice between a phone-sized screen and a tablet-sized screen in a single device seems personally desirable to me; I don't really care much about the device size itself as long as it still fits in my pocket (unlike the tablet it'd be replacing).