This is the only fly spray I use on my horse. It's oil based, so that's where the longevity comes from. I wouldn't say it lasts 17 days, but I think we have a little lead time on the 17 mins :) (what kind of crazy bugs live in NC anyways! hehe)
Personally, the citronella smell doesn't bother me, and I did like that the product lasts longer than the water-based products and since my horse has free choice turnout, I am confident that he is not getting pestered to death by those stupid biting gnats!
I don't think its unsafe to use, but in the grand scheme of things, how many flysprays are if they are capable of mass-murder? ;)