I rely a lot on user-modes in my workflow. But the mode you have, the more it is to find them a quick access key.
So, for the one I use only once in a while, I found that the following alias helps a lot:
alias global u enter-user-mode
This way a simple
:u<space> the autocompleter kicks in and all the user-modes are easily available.
Kakoune offers a few 1 letter aliases by default (
b…) but adding other ones is handy for quick access.