I use the riffle hitch quite a bit on the Gaspe with a great deal of success. I will point the fly upstream and then tie 2 half-hitches so that they come off the bank-side of the fly. I find that this is effective for 2 reasons. First, the second hitch keeps the first one from slipping off. Second, the fly planes just in the surface and the v-wake is very pronounced.
As far as hooking the fish goes, my experience is varied. Sometimes the hook ends up in the corner of the mouth, whereas other times the fly ends up in the middle of the mouth. I never figured that out until this past season. I had a couple of guys fishing a small pool on the Grande River. The run is narrow and has an easy flow of water. The angler was working his way down and I was 30 feet below him and 10 feet below where his fly was swinging.
As the fly came across the run a grilse rose straight up, stuck his head out of the water, and took the fly. What is memorable about this take is that when the head came out of the water there was a "pop" sound that was made-- just like a bluegill makes on a popper. The other angler and I wacthed this whole episode and started laughing when we heard the "pop". Ironically, the angler was looking into a glare and could not see the fly or v-wake but heard the take!
The other observation I have is that when a salmon takes a hitched fly I see the head and back out of the water; it is pretty amazing. One word of advice; don't set the hook when you see the head and/or back.
Malbaie River Outfitters