I think your getting 2 products confused.
The FSE biist kit is designed to increase your fuel pressure by restricting the flow back to the tank. This means that when you mash the trottle, there is lots of fuel allready at the injectors awiating to be squirted

, this does help iron out flat spots and makes throttle response better.
The device that makes the funny noises and is suposed to give you better MPG and power is an echo valve. I have seen several test done on rolling roads, and they have all seen a small increase in power and pick up.
So, is the FSE kit worth a ton, do you have any flat spots or slugish trottle response? only a real advantage if your engine is tuned and its setup on a rolling road.
Hope this is of some help.
craig
PS if you do fit one, make sure your fuel lines are in good shape, the extra pressure will find any weakness.