Used mine once that I know of...on gravel. I think it's one of those things that becomes a personal preference item. For me, it's my personal preference to have it and if/when I get another wing it will have ABS.
I used it on gravel coming back down from the north west road into Mount Rainier National Park. Dirt and Gravel. Kept me from sliding the back end out from under the bike. I also tow a trailer and while I have not needed it yet with the trailer on behind I am glad I have it after feeling how well it works on gravel.
All European Spec Wings come with ABS and I have on a few occasions had it kick in. Wouldn't want to be without it now, since on one of those occasions I do believe I would have otherwise gone down with the force of my braking, caused by someone else's bad driving in front of me.
I too have had it kick in on loose gravel on roads and whilst it is still a slight pucker moment, I would prefer that to the alternative, without ABS. :shock: