I've just gone to double & bash – Got a soul and found during some rough stuff the chain drops off occasionally which is annoying, I also find that it drops into the granny ring accidentally but I think that is my thumb knocking the shifter rather than anything else.
I've swapped the big for a bash as I only really used it on the road and that was like once a month at best and plus when I came off I've had too many calf / big ring moments and this just makes me less worried about it.
I'd like to get a chain device but gonna see how I get on with this first – but this doesn't really answer your question does it…