You've got to go with what works on you. Personally, I hate to put chems. on, period. Especially if I can't wash it off soon. But when the conditions are real bad, nothing else but Deet products work on me. The lower the amount of Deet (7% - 15%) the more often it has to be applied. Good for short term use. Deep Woods Off lasts a lot longer & is probably the best for most conditions. But I will admit, I put just a couple of drops of Bens on in camp once & spread that sm. amt. all over arms, legs, & head areas & they stayed away, period!
As far as non Deet products on me, forget it. I've had people swear by things like Skin so Soft for Mosquitoes & Midgies (at the Marina). The perfume smell nearly killed me & I think I got bit more, so I wouldn't even try it for black flies.
So if your going out, especially overnighting, take some Deet & try not to use it, unless your sanity depends on it. (I actually saw a guy almost loose it once).
I have some plans this year to overnight during Black Fly season & I'm getting a head net cause the Chems. are real dangerous for me now. I'll still take some Deet, just in case.