Game flagging from bright fletch on a bow quiver is pretty annoying and like Mint I've found that out the hard way several times on deer.
To be honest I've never seen a fletch cover that looked like it was worth buying. Most seem either too loose, too noisy, cumbersome when removing arrows, overpriced or some combination. I generally just pull a spare headnet over my fletching and secure it with the elastic strap on the headnet, use bland feathers except for the #1 arrow or use a different type of quiver that doesn't flap feathers like a beacon when my bow moves. The closest thing I've seen to fixing this problem that actually works well is a Catquiver.