I've heard explanations, basically once you get used to this type of keyboard, the fact your hands don't move to reach the further keys lets you type much faster and with less fatigue.How do you even use this?!
I can't think of an usecase where such ridiculously small keyboard could be the main (and only) keyboard in a setup
All symbols and functions are available through key combos, and since all of these keyboards are custom, you get to set it up for just the symbols you need/use and arrange them however suits you best. The use case I saw was for Linux/Vim, but there are other uses.
It didn't convince me to leave my full sized keyboard but I guess some people might prefer it.