Custom should be understandable for everyone, and I don't see why it
isn't. It works reasonably similarly to, for example, the Mozilla
Firefox about:preferences page.
Some people only feel that they understand a program when they are
able to make a good mental model of how it works. And to me customize
is a big black box with several smaller black boxes inside, and with
no visible tools to let me inspect its data structures.
[[]], E.