(Only tested on PW-3, 5.6.1.1)
There was a problem running 2.2 from the KUAL Booklet.
The first time, it appeared that the keyboard was not working and no response from the touch screen.
It only **appeared** to be hung - after a 3 or 4 minute delay, the characters previously entered showed up.
Problem cleared before I could get a clue of what was happening.
Note: The main screen of the Kindle is also a Booklet, and in the early days of the paperwhite series, you could input faster via the touchscreen than the Kindle could respond.
So the above might just be a reoccurrence of a previous system problem.
To answer my own question above:
The application start-up and response is noticeably faster under the KUAL booklet than under the KUAL document.
A note on that: You can install both, they do not conflict with each other.