I generally use Phaser...works very well...but no the smell isn't great but it really does keep the flies away and any other bugs as well!!!! Also you don't need to use much, it seems to last for ages.
I have also got the Mark Todd one...which is nicer smelling but don't know how good as yet tbh...
I use Coopers Fly Repellant Plus, put it on twice a week and he's never been bothered by the flys, you can see all the others in the field are being harrased by them, it also kills mites and lice too so there must be something in it that is pretty nasty to keep the little buggars away.
Also used a fly sheet, so the combination of that and the Coopers also give his coat a lovely sheen too!