The fourth switch is the LED on/off switch. The quick tone change switches act as a boost (from what I can tell) for treble and bass. The third switch is the Q on/off switch. The only thing I would change is having separate volume controls for both pickups - a legacy of playing Jazz Basses for so many years. The pan isn't bad, but I'm not used to it ... yet.
BTW, had my final gig with the band I was playing with in the DC area on Sunday, and I used the Europa. Had to play it through an Eden 2X10 amp, but man, was it awesome. Very comfortable to play, unlimited tones ... makes it hard to choose between it and my Spyder (didn't have enough room to use the Spyder!).
Anyway, thanks for all the kind words, guys.
Best regards,
Alan