I got my Kemper in mid-October, just under 3 months ago. The build and user interface are excellent, everything you need to do is intuitive once you learn a few basic ideas and functions. The manuals seem a bit thin but when you get your hands on the various modes they are completely adequate. In particular the profiling process is pain-free and very straightforward.
The machine comes with about 400 profiles but I have to say most of them are not my cup of tea. Something I have noticed with third party profiles is that many are specific to other players' taste and too many have very heavy effects laid on top. But fear not, if you have an amp that you love you will capture it in the Kemper - probably several times for different settings - with no problem. I have a dozen profiles from a Marshall JMP-1 and several from a Mesa V-Twin that sound exactly like the original to my ears. One caveat (maybe this is just me) I do find humbucker guitars work better, but then I did do the refinement on these profiles with humbuckers, so maybe that's why.
You will probably want access to profiles you can't make yourself and there are literally thousands available, many free, some commercial. I chose a bunch from The Amp Factory where you can listen to them before you buy. Managing the rigs on your Kemper is a bit of a palaver but anything is possible (remember to back up what you want to keep) just work logically and organise your folders on your computer.
So overall, I'm very happy with it. The test for me is whether it can make you want to play like your favourite amp, and it does that. I recommend you spend some time learning how it all works and going beyond the presets to find profiles that fit your style.
Edit: About single coils v humbuckers: after some more profiling and more experience using different guitars I think my reservations are about volume levels. When you make a new profile the Kemper automatically sets the levels—adjusting these afterwards can be rather complicated. So if you use a single coil guitar with a profile made using a humbucker you have to turn it up, with varying results. Profiles made with single coil guitars (and amps etc. set accordingly) work fine for single coils, as you might expect perhaps—I did say it takes some time.