I would choose a net over chemicals, however I've found that either are only effective to a certain point. While you can't stop flies, you can change your reaction. If you can find it in yourself to shoo the most pesky ones, and tolerate the masses, you might be able to concentrate on the other more enjoyable aspects of the great outdoors.
I base this on 6 years living and working in Central Australia, I spend alot of time outside, and out bush.