Tommy the Cat, I tend to put my trust in toxic chemicals, as I like the reassurance of seeing mosies and midges spinning out of the sky 6 feet away.
I use Jungle Formula and for some irrational reason prefer the absorption method to inhalation. Either way, none of these things can be good for you, as has been well proven. Today's Jungle Formula is a mere shadow of the stuff as it was sold in the 80's, which in turn wasn't a patch on the 80% DEET I got from a Squaddie in Glencoe.
There are DEET free products available, one recommended to me is called Skin So Soft, which I bought for my wife to use. It did seem to work, although it has to be applied regularly. The proof was when she went for a shower at a campsite (not my choice) in Arran and, forgetting to put the stuff on again, was was eaten alive within minutes.
I've used the coils you're asking about but find them more effective against mossies than midges in the open. That may be something to do with the sheer numbers of midges in some places.
The coils are really designed for indoors and they do work. It's the thought of actually breathing the stuff that bothers me!