I can't say I've noticed any difference in break-off rate w/ droppers. I almost always use barbless hooks, and I have noticed that I do tend to lose the entire dropper rig because it slides off the hook point. Not an issue if you're smashing barbed hooks.
I have wondered though, if a smashed barb might compromise the integrity of the tippet for a dropper tied off the hook bend as it contacts the point of the smashed barb. I've also assumed that catching or even missing a fish on the dry could be nicking the tippet for the dropper(s).
I've tried all kinds of different rigs in terms of droppers. I'm lazy so I hate tying tags. One thing I'm experimenting with currently is a loop of 5x fluro tied into the body of the dry and camouflaged by the shuck. So the tippet for the next fly is tied off the hook bend w/ a clinch knot and runs up through that hoop of 5x.
My theory with this contraption is that it keeps the dropper line from either sliding off the hook, or getting wrapped around it, or in the way of a fish eating the dry. I've seen klinkhammers tied with a tippet ring tied into the body which inspired this experiment. Disclaimer, I haven't used these flied long enough to know if they're any good. Just a fun little side project I'm messing with.
sorry for the crappy pic. You can barely make out the 5x loop with all the CDC and flash. Exhibit A:
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