After an 'interesting' day riding a horse at a dressage competition a couple of years ago where there were a LOT of horse flies which didn't bat an eyelid at the stuff we were using we did a lot of fly repellent research. We ended up finding some stuff called icaridin/picaridin (chemical name) and that worked really well.
I have since sourced the active and make my own and it is the best stuff I have used with horses. Doesn't smell and just works.
Smidge contains Saltadin which is the brand name. Basically look for repellents containing Saltadin, icaridin or picaridin - it is all the same stuff.