I have been making and shooting spiral flu-flus for over 45 years. I think they perform as good or better than 4 or 6 fletch full height feathers.
I use heavy paper clamps and a bead of DUCO all the way down the feather. (clamp the nock end and spiral down) finish out and clamp. When dry, I trim with a razor knife and arap both ends with the narrow electrical tape. Then the feather will not lift from either end with a lot of use. I prefer just one full length feather. I get about 50-55 yards of flight in a 55# bow. I find the double feather to be too much work and too much drag. The first 25 yards is pretty fast. I try to hit my target in 15 yards or less.
I haven't hunted birds in quite a few years, but in my younger days I scored a number of ducks and pheasants and 1 Hungarian Partridge. I won't say how many birds I missed, but with a good flu-flu you won't lose many arrows!