I’ve got a KP3, not a Quad, but FWIW:
It will definitely give you more effects, and more instant gratification than the OT/Xfader approach, if only because KPs are plug & play, requiring little or no setup to get started. Just be aware the quality of the effects is not the greatest across the board and pretty cheeseball in many cases. To my ears, a handful of them have “sweet spots” that I save and recall. That’s half the reason I keep the KP3 as part of my live rig: It is indeed great in a live club setting and audiences love hearing something happen when you perform on it.
The other half is because the KP3 has samplepads and MIDI, so you might consider that model instead depending on how you envision using it for transitions. Housecliche is spot on about it being a good source for occasional color, but if you don’t want to burn a track on the OT for recording/looping, the KP3 will fit the bill for that too: If you slave its MIDI clock to your OT’s, you can sample CD-quality loops from your performance that will stay in time with your groove for a couple of minutes. Plenty of time for a DJ-style transition. I’ve done a few gigs recently with just a MDUW and a KP3 and it’s been great.