I've owned the RC600 for about a month now, so I've had a good chance to get used to it.
First off, I'm extremely happy with it! My set up is
TC Electronic Polytune -> Crybaby Wah -> Helix HX Effects -> RC600 (with Boss FS7 as a Ctrl 1+2)
Plugged into it I have 1 vocal mic, 1 acoustic or electric and 1 cajon.
All of this is powered by a single Cioks DC7. I'm using the Cioks 8800 Parallel Adapter Flex with a Cioks 1050 Flex Cable Type 1 to get to the milliamps needed. Powering up, it can get to about 70% load on the milliamps, so it's perfectly safe with that.
The routing is a godsend. I've got the main output set to the vocal track. The guitar on sub 1, the cajon on sub 2 and the click track on the phones out. All isolated outputs. So this is great if you're needing to mix your sound to the venue on the fly, record to multi track, or hand individual instrument outs to a sound guy.
I only need 4 tracks, so I've re-assigned the track select and undo buttons to be track 4 record/play and stop. The RC600 is very customisable. You can assign any function to any pedal.
However, the one and only critisism I have for it is the lack of scribble strips. I ended up having to put tape over it to write on what I've changed the 2 pedal functions to. I also put tape on the middle track as that's where I put my drum track. It would have been much easier to type the names of each pedal assignment on a scribble strip.
The size is much better. I never needed the expression pedal, so I'm glad that's gone. I much prefer the setup of having the option, rather than forcing it on you.
I use the Helix for my effects, so I haven't tried the RC600 effects.
The menu is a lot easier to navigate. Everything is laid out a lot more intuitively. The rhythm track is accessable in 2 clicks.Tempo in 1 click. You can get to the measures quickly and cycle through each of the 6 tracks easily for each individual track's settings/recording options. The ability to only record what input you want to a certain track keeps your mix clean and reduces the chance of mic feedback. It saves you needing to have a mic with a mute switch too.
The track bouncing is a great feature for streamlining performances. I've laid down the drum beat on track 2, recorded a verse on track 1 and then a chorus on track 3 all while bouncing the drum track to both 1 and 3 so that I don't have to start multiple tracks when needing to start/stop sections.
All in all, I'd highly recommend it for any looping artist.