Some more early thoughts...
I haven't dug through 100's of profiles but I'm mostly sticking to the MBritt stuff I had before. Sounds great playing through headphones or monitors alone. I've not spent a lot of time messing with effects, but the reverbs and delays sound pretty good for general usage. I spot checked a few of them against HX Stomp and the chorus, delay, reverb etc. are pretty good. The stomps aren't quite as good, HX Stomp works better, and real pedals are good as well.
I recorded some tracks for a song idea over the weekend using the Axe FX 3 and Kemper, and already had dry tracks set up with NDSP. The Kemper tracks are noticeably darker and fatter than the others, and the first ones I picked were completely lost in the mix. That was a bit odd because I dialed in the Axe 3 tones the same way (sound good on their own) and they stood out in the mix nicely.
I found different profiles and boosted the mids/treble a bit, and now the Kemper is sounding good, although still pretty big sounding in the lows. It seems this was an issue others ran into, where MBritt stuff sounds good solo or live at high volumes, but not as much for studio tracks in a mix. So I may try some of the other profile makers who have tones that sound brighter or thinner on their own.
After I installed the beta for 9.0, I did several tracks with the USB Audio feature, which worked really well. There's two output tracks and you can pick what you want to record. So you can do stereo outputs like normal, or DI dry signal and mono, or what I did was DI / mod mono which is the profile without post amp effects. That way you can monitor with time based effects but record basically a regular amp and then add wet effects in the mix.
Also briefly tested audio playback which seemed to work fine, and you can control the input level so you can do direct monitoring with no latency and record signal at the same time. That means you can record without an audio interface which is really cool. It's not as portable as the HX Stomp by any means, but you could just use a laptop and Kemper head or Stage to do guitar tracking pretty easily.
Still need to run it through a power amp/cab, and still need to tinker with more effects stuff, but it's a good change of pace unit for me right now.