I've had mine for a week and a bit now & I really like it. I've owned a Line 6 HX Stomp, HX Effects, Fractal Axe-fx, Axe-fx II, AX8, FX8, and FM3; I believe the Quad Cortex is the best out of all of them.
I like how it keeps its functionality on the more simplistic side like the Helix stuff and doesn't get super in depth like Fractal does - which is cool, but I could never stop playing with all the options long enough to really play (definitely user error, not a gripe against the product itself).
I have never owned a Kemper so I can't compare the technology they share, but I will say the capture function is pretty friggin' incredible! I'm a bit of a dolt when it comes to this, so I currently cannot for the life of me figure out how to capture my real amps while using my Boss Tube Amp Expander rather than a cab/mic set up, but I keep searching it every few days to see if someone uploads a video or something explaining how to do it.. facepalm.. Anyway, capturing pedals is very straight forward and even rewarding! I have been able to capture some of my favorite boost/OD/distortion pedals (that will probably never get on Line 6 or Fractals radar) with great success; a little bit of tweaking from their added digital EQ and a couple captures I've been able to make indiscernable from the real pedal. The ones I couldn't do that with sound so close that in a mix you can't tell at all, which I think is a huge win in its own right, without having to compare it to another product.
I like how it's powerful enough that I'll probably never reach its limitations in what I'll actually use it for at home or if I ever get to play it at a real show.
One neat trick with the QC to keep memory usage down is to actually capture an amp or full rig set up (if you prefer FRFR) and use that as opposed to QC's own amp/cab/boost pedal/etc set up. The reason being that the capture takes up much less usage on its own, and still gives you everything. You could make a capture of your rig boosted, then a capture of it not boosted, and use scenes to switch between the two captures & it takes up less memory than the traditional digital set up I mentioned earlier where you'd just be turning the boost on and off.