These parabolic boosters don't work as good as the hype surrounding them.
I did some field trials last October in a very flat and open park in Ohio. I did 5 flights without the parabolics and 5 flights with them under the same weather conditions and leaving all settings identical on the bird and controller.
Basically, I was only getting about a half mile further distance with the parabolics. My max. flight distance was 1.9 miles with them.
So in a nutshell, spend your $10 and get a mild improvement in distance. For real distance, you need something like the FPVLR kits.