i had one and hated it, but sounds like i'm in a minority.
it did have plus points, which were a very comfy ride for the baby, nice and snug in the winter, if you buy the footmuff and the seat unit does lie flat, so you don't really need the carrycot. also looks great, which is why we got it (DH being a gadget lover)
HOWEVER, the downsides for me personally far outweighed this and they were:
it is very bulky and heavy, hard to fold up, takes up a lot of room, so unless you want to disassemble it every time you put it in the car you need a big boot, which we didn't have, so i used to have to take 3 or 4 trips to the car to get the frame, then the wheels, then the seat unit, and then the baby...
the whole thing folded, with the seat unit on weighs A TONNE. 12kg. you can only fold it with the seat unit attached if the seat unit is facing forwards, not if you have turned it to face you
also, the opening mechanism is lethal if you accidentally put your finger in the wrong place, as i found out to my cost. got my fingertip stuck in it and a) couldn't get it out without help and b) it was properly bruised and lost feeling for a good few weeks
also, the harness is rather short. DD had it on the maximum setting by a few months old
the storage underneath is tiny and has to be bought seperately. the changing bag is in the strangest position, and you end up kicking it as you walk. and you can't hang anything from the handle
anyway, we ended up getting a light buggy in the end (mamas and papas aria, which looks nowehere near as good as the quinny, but which DD loves), and with hindsight i would have got a cheaper travel system where the car seat clips onto a stroller. the fact you can clip the car seat onto the quinny was a big selling point for us, but actually cheaper travel systems do the same thing
i now know why you rarely see anyone with more than one child with a quinny buzz. lovely to look at, not really practical day to day unless you have a massive boot and very strong back