There's no loss of speed if you put them mid limb either. If there was, you CAN make up about 4-5 FPS on average using crank bait tails instead of cat whiskers.
At least I didn't lose any speed on my setup, with and without them. The difference in noise was substantial. That was shot through two Shooting Chrony's in tandem, in my indoor 22 yard range with good artificial light BTW.
What kills me is how many "speed freaks" chronograph all day at the back of the bow, and never see how much a radical helical on 5 1/2" nanners at 120 degrees slows down an arrow at 20 yards.