> You'll have to build emacs from master to usue it.

This isn't true though.  I've backported it to 27.1 by copying the definitions
of `undo--last-change-was-undo-p` and `undo-redo` into my init file.  Works
great and might very well replace undo-tree for me (I've had random hangs with
it lately that make undoing text a gamble).