I'm on the waiting list. I already have an FM3 and enjoy playing it at home and with one particular project. When I'm out doing bigger shows, I take the Stage and a couple of Kabinets; can't beat it for ease of use and set up. I also have an HX Stomp for jamming and putting down quick guitar lines at work. They're all great yet different solutions. I would probably be happy with just one of them, but where's the fun in that?
For me, the Kemper is an amp and pedalboard replacement. It just sounds and feels more organic to me, whereas the likes of the FM3 is more like a studio rack set up, in both sound and routing possibilities. Horses for courses. I enjoy shredding 80's style on the FM3 more than the Kemper, though.
Can you explain why shredding is better on the FM3 while the Kemper sounds more like an amp? Because of better delays/effects?
I recently tried the NDSP Petrucci and really it sounded better than my Kemper for Petrucci's tones. But it didn't FEEL as good.