we (seaford) have a 500L slip-on for our logistics car, but region wont ok it for use on the fire ground, so instead it is used as a pump trailer, and almost never leaves the station.
one great thing about it is we can put it on and take off the trqailer with 4 cadets!!
As for the effectiveness of QAV's from what i have seen they are awesome on the fireground as the can get in under low branches etc. without ripping lights off the roof.
*Pixie*