The "off side" works as fletching, but is usually pretty short on primaries. Like Pat said, the offsides of right wing feathers will be essentially left wing feathers, so don't put both sides on the same arrow. I have used them a few times with good results for arrows with field tips. You usually don't have to trim them down to height-just use them as-is. I remember reading an article in one of the PA back issues about archers in (I believe) Bhutan who considered the offside of the feather to be the primo side. They do a lot of long range target shooting, so they like the low fletchings.