I've been curious about it, and impressed by how it seems to condense and intensify light reflections.
This Flashabou is the one called Lateral Scale that is crimped into a zig-zag, breaking up the reflections when laid straight. But when wrapped around the hook, the crimping doesn't show. I guess it is intended to be used in a straight line, on each side of the fly, or streaming.
There have been a lot of flies posted here with flashabou, so this is just an addition to that group.

Hook—14 Jim Bashline Wet Fly (Gaelic Supreme)
Silk—ash
Hackle—Dark grizzly hen
Rib—lateral scale flashabou
Tail—lemon woodduck
Body & thorax—muskrat tips on ash,

Hook—12 Jim Bashline Trout Wet Fly, Gaelic Supreme
Silk—ash
Hackle—rusty dun hen
Tail—lemon wood duck
Rib—Flashabou, lateral scale
Body—pale brown Argentinian hare on ash

Hook—12 Jack Mickievicz Letort Dry Fly
Silk—gold
Hackle—speckled hen dyed yellow
Tail—lemon wood duck
Rib—Flashabou, lateral scale
Body—golden olive embroidery wool, single strand
Thorax—bronze peacock herl, two strands
When I bought this Flashabou from Mike Hogue, Badger Creek Fly Tiers, he asked whether my father ever would have used it. I honestly don't know the answer. I suspect that he would have tried it, but we'll never know.
Lance