I've done quite a few, used to be on our dairy with Holsteins. I prefer using bands on the horns if they've gotten away on you, but the BEST way is to use an electric dehorner when they're baby calves... like less than a month old. About the same "pain factor" while doing it as branding... but they're over it as soon as you let them go pretty much... an hour or so of head shaking... but for the most part, it doesn't set them back at all.
I have the elastrator tool with the "green Cheerios"... and I agree that they can tend to roll off pretty easily, and the XL bands being squared off don't do that as easily... but that makes them harder to "roll up" then too (I've used them both). On animals with a steep taper on the horn, I too have cut a notch into the horn at the skin/hair line to "set" the band into. You don't have to do it all the way around... just kind of on two opposite sides, and just enough of a notch to ensure it can't roll back off. They'll bleed some from that cut, but once the band is installed, that quits pretty quickly. Horn will fall off in a few weeks to a month. Lots of times, they will knock it off just a little prematurely as it dies... and then they will bleed some, maybe for a day... but it's never too bad, and can't be as bad as gouging them.
The "green Cheerios" seem to want to tear pretty easily... which is never a good thing. The elastrator tool that stretches them can begin that tearing process because of how it puts all the stress from the stretch on just a few very small points... so look at that thing before installing, but after you've stretched them out fully... Do a number of hand squeezes on the tool to stretch the band and work it up gradually to fully opened.
I had one fairly large calf (about 300#) that I was just able to slip his nuts through the band on... and durned if that band didn't break about halfway through the job of nuts falling off... calf developed a large grapefruit sized mass right below his belly, stunk bad, looked pretty rough, nut sack hanging down about 12" below that .... thought it might have been a hernia... regardless, I took my California banding tool (with the surgical bands... should have used that one right from the start), and wrapped around the whole thing right up tight to his belly... figured he'll either make it or he won't... but I wasn't sticking a vet bill into him yet too. Gave him a tetanus booster (had given him the first dose when I banded him the first time). In a few weeks everything fell off, he quit stinking, started picking up on attitude, and today, he's as good as can be... you'd never know he had a problem at all, and his underside is nice and smooth... no telling it even.