I use the Deo lotion (in the orange bottle) and it works OK I guess. My trimmer recommends Ricochet, another one made of essential oils.
One I wouldn't use on a sensitive horse is Pyranha. My horse usually isn't sensitive to anything but he HATES having that sprayed on him and several people on this list have had sensitivity problems with that one. It's a shame because it works better than some others I've tried.
With my chestnut mares, I always shop for water-based repellants. Those with an oil-carrier will keep the product in contact with the skin longer, leading to allergic reactions, either to the oil itself or to the repellant ingredients. Water-based sprays, in my experience, last long enough to get the job done without triggering a reaction. My favorite of the moment is Bite-Free.
"Avoid loud and aggressive persons, they are vexations to the spirit."
- Desiderata, (c) Max Ehrman, 1926
I get from Jeffers Equine Bio-groom fly spray. It is baby powder scented, and it is not high on the chemicals to irritate my fly spray sensitive horse. She actually likes this spray. Maybe it is the smell, maybe it doesn't sting when it goes on. She does, however, understand fly spray keeps bugs off of her. My little old lady horse of 20 plus years old also does too.