I posted my preference on jet kits in your Jet Kits thread.
Why do it?
The factory FZ1 carb set up is lean at the bottom and rich at the top. The jet kits balance that situation out.
With the kit, the low-end power comes on MUCH stronger and smoother, and the top end smooths out. With the corrected fuel / air mixture, You should see improved fuel economy AND better power delivery. I remember the serious eye-opening difference as soon as I let the clutch out on my first ride after the kit. I was loving it immediately... I never expected that dramatic of a difference.
As for the switch, mine started to jam slightly and I just added a quick shot of WD40 in the key mechanism, turned the key back and forth, and then shot it again, turned back and forth. it seemed to free things up nicely.