Deet won't touch them.. Most of the "remedies" around here are vanilla based. They'll work, to some extent on a mild infestation. When they really get cooking - nothing (I've found) will keep them at bay, short of wind or a full head net.
I've never seen Germ X in this part of the country.. I see Ethyl Alcohol is the active ingredient.. I need to check that out.
I never knew if the infamous "black flies" of the north were the same critter. I googled it.. May order a bottle of one or the other "north" repellents.
Oh, and Barry.. those ankle biters.. I have a fly swatter in the boat and carry a can of Dairy Bomb for when they really get bad.. I never realized how many freaking biting bugs we fight.