Lets not forget that this is a Kemper forum. The opinions would be radicaly different if this was a Neural DSP forum.
I have been using a Kemper for 5 years and had all possible form factors Head, Rack, Stage, powered unpowered.
I also use several high quality plugins, including Neural DSP ones and Helix Native (the plugin version that has the same features as the hardware units).
I also own and have used several tube amps (the most recent, a Diezel VHX that really covers both the traditional real tube and the modern apponitments like presets, effects, IRs...etc).
And I have also a Quad Cortex.
My opinion on it is that it will be a great unit, but it is currently lacking in some vital features to really go against the best digital units.
For live use the output options are going to be updated but right now it is not possible to have several outputs selected at one time, which for instance makes it impossible to have a separate output for monitoring and another one for FOH.
Other important thing for live use is that there is a cut in sound between presets (this is normal in all modelers) so you have to use just one preset per song if you don't want the sound to be cut. That leaves you with the SCENE mode (like the snapshots in Helix) that works good but the amount of things you can load into a preset has some limits. Actually more limits that what they marketed(they told you could run a complete band thru it), but this will hopefully improve with firmware updates.
The current effects are ok, but all the other units are way, way better in terms of variety and in some cases quality.
But it all depends on what effects you like and use. For instance, the Pitch Shifter for single notes (not poly) in the Quad Cortex is the best I have tried yet. Way, way better than the Kemper transpose. It has almost no latency and keeps the real tone quite well.
Flanger on the other side is kind of... terrible.
The form factor is great. This is possible because the foot switches are pots and also you have the touch screen. Probably one of the best things of the unit. It is very portable, but also very powerful for it's size. At the same time the touch screen is far from being as responsive as any android phone or iPhone.
USB audio is a nice feature, but not for serious musicians that will likely already have an audio interface working on their system and with monitors connected to it.
In the end it's just easier to connect to the audio interface.
On the other hand, lack of SPDIF is quite bad.
Sound quality of the modeled amps depends on the model. Some are very good, some are mediocre. Not outstanding.
I have not used the factory captures. No opinion.
I have made some captures myself. I captured my Diezel VHX both with an IR and also DI. The complete amp+speaker sim sounds GREAT. Impossible to tell appart and very easy to make. A lot easier than creating a Kemper profile in my experience. The DI capture, without an IR is completely disappointing and sounds completely different from the amp. Unusable.
I also made a capture of a Klon clon pedal I have. It did capture the tonal characteristics of the pedal. But failed to get the gain and the volume of the setting on the pedal, making the capture unusable (gain and volume on an overdrive are the key to get the amp react the way you want).
The best thing about the capturing is that it has almost no variables, just input volume, and no tweaking. So it is very consistent. Profiling with the Kemper is not as consistent and can get great results or terrible results.
I feel that with the QC there is going to be a lot of cooking in the captures world, the same way as in Kemper. And with time there will be great captures for sure.
But currently the sharing software cloud system is TERRIBLE and the amount of available content is small and difficult to find.
So, is the QC better than the Kemper? Currently a very easy NO. But if you need a small unit that can do a lot of things and you want dual amps, that the Kemper can't do... then you might think it si better.
Over time I see that Neural DSP has a lot of room for improvement and I really see how it will be a real force on the model world. And it already is a market success with all the units sold out on any retailer.
What could do Kemper to improve their current devices and match what the QC offers?
-The touch screen they already have it covered with iPad app.
-They would need to create a simplified profiling method. Maybe have two methods, traditional one and simple one without refining and consistent.
-Release a smaller form factor unit.
-More flexibility on the number of stomps or effect before or after the amp.
-Dual/triple/cuadruple amps in paralel. Some people like to do this and the Kemper is not able to do it.
-USB audio
-etc
There's probably more to all this but, there you go. I tried to be the most objective possible.
By the way I am currently using more and more the Diezel VHX than any of the modelers or plugins including the Kemper.