Put one on my Z51 coupe last fall I found that it seemed to respond better with more air flow, not sure how much HP I got. Did not do a tune or dyno. But I would say it's worth the money I went with the dry washable filter.
I haven't seen that, but Halltech has also been claiming huge gains on the Z06 with a CAI. Looks like a bunch of easy cheap horsepower on a Z06.
Much different on a Stingray I'm more inclined to believe Halltech (whose claims are much lower on a Stingray than AFE's) because so much dyno work was done by Katech. See Halltech's site on that for more information.