I been playing around with the quick fix, seeing just how well it does work.
The twin jumping has it's uses, but it is extremely hard to maintain a link to a demo or soldier. you just don't know when and in which direction your target will be jumping. Saying this a practicing pair can easily use it to great advantage, one quick example.. demo rollout on viaduct, if you play hl you will know that a good demo is just about first on the point, and first to need heals, going in with him will keep him at full heal, keeping your first line of defence forward of the point. This also negates the need for overheal.
Also using viaduct again as an example, the charge of the quickfix is really quiet useful, multiple targets on the point, charge with the pyro (instead of the usual demo/kritz combo) can have devastating effects.
I have even used quickfix to charge multiple enemys with scout (you do need a half decent scout) if you think how powerful scout is at close range, the QF allows scout and medic to get right up close.
The downside to QF is obviously taking down sentrys is very difficult, snipers pose a problem too, so does any crit that does a decent amount of damage, but these are problems that concern the kritz as well, infact kritz is weaker in this area.
All in all I think the quick fix is on equal par with the kritz, for KOTH, defense, and some points of offence, however there are some points where the ubergun cannot be replaced (blocking an enemy uber for example)
I've yet to use QF in a hl match/lobby just for the fact that I would get so much shit from the rest of the team, because of the QF's stigma.. however a bit more practice and I will give it a try.