I spent about a year using the Zoom b6. Really straightforward great live board, good built in DI. If you are just looking to expand out a little from a zoom B3 it has to be an option. Modelled amp, and DI with about 4/5 effects and a brilliant tuner, it is pretty much everything I needed at the time for gigging in one box. Moved to a Line 6 HX stomp XL as I was looking for the effects to go more 'out there". I have used it live, once set up it sounds great but I'd say it does need a fair bit of set up and potentially tweaking on gigs more than the zoom did. Yes its a more powerful beast and can do allot more, I'd say its a question of what you want. With the Zoom i edited and set up usable patches by plugging it in to my amp and just tweaking. With the HX Stomp i had to plug the laptop in, and the amp and then do it.
I think we are in a lucky position that the multieffects/modelling market has a load of great gear, its down to how you want it to work and how you prefer to edit work with it, sound wise I think you are unlikely to go wrong.
jonny