All that stuff says it is, is veeeeeerrrrrry expensive “conditioner”. A tiny amount in a tiny bottle, with a whopper of a price tag. I would think that any of the MUCH less pricey horse tail specific contitioners would do just as well. Matter of fact, if I wanted to condition my own eyelashes, I’d just put some pantene or biolage on 'em in the shower with my eyes closed, then rinse. I’d think conditioning eyelashes would be of limited use, however.
There is some other stuff for eyelashes that is prescription only, drops that you put in your eye. Not sure how that works but doubtful it would be absorbed by a horse’s tail skin. You’d likely have better luck with rogaine…