I own both -- the AxeFX II, and the Helix. Agree that the Helix doesn't *quite* match the AxeFX in terms of tone, but for the gigging guitarist who needs a stage tool rather than a studio one, the trade-off is worth it for one simple reason: USER INTERFACE. I'm not a complete idiot, but in 4 years of owning an AxeFX, I barely managed to scratch the surface of what it can do--because it's impenetrable. Some of you are probably very technically minded, and that's great. AxeFX is an astounding tool for you. But I can say truthfully that I am already sounding WAY better live with the Helix than I ever did with the AxeFX, and it all boils down to how easy the thing is to use.
That being said, now that Helix has taught me a thing or two about signal path design, I'm tempted to go back into my AxeFX and see what I can do...but the ease-of-use case for Helix can't be overstated. For $1500, I have a powerful signal processor that--while it might not meet the high standards of the Axe community--fools a LOT of people into thinking it's a tube amp, and a remarkably intuitive control center for my entire rig. AxeFX demands $2k+ just for the box...and then, if you dare to use a controller other than Fractal's...bad times abound.
Like I said, I'm sure the engineers here can manage in the live setting with the AxeFX. But even given the [modest] tradeoff in sound...I doubt I'll go back.