i have seen ats has one but dont know how they work or who else makes them
any of you all have them or are they worth it

 

they mainly cut back the air that goes into the afc housing, that prevents the foot in there to slide forward once it gets boost.
so it doesnt fuel any harder at boost, then at 0 boost,
a 800 hp truck, makes aaround 500 hp in valet
a 500 hp truck around 200 hp or less in valet, it all depends on starwheel adjustment, and how the afc is slided, forw or back.

look at the other valet switch thread on here,

piers has them too, they work with an electric solonoid vale.

I'm makin one with a regulator with variable fuel output.... fro smoke control