It has always worked perfectly for me. I have that box
and the
"Enable system tray icon" box checked (and qjackctl saved in my KDE
session), so when I start KDE I have a small plug icon sitting in the
system tray from which I can get to the connection window, and jackd
is started and ready to go.
same for me. Added qjackctl to the KDE autostart folder (I personally
dislike seesion management) and it works very well this way (except the
USB audio card isn't available ;-) .
Best regards
ce