Never heard of them called "Chicken Slides". . I've always heard them refferred to by the big rigs as "Chicken Wings". Either way, I have the Taylor Oversize for about 10K miles now. Pricey, but I got it on sale and picked it up from the factory.
Like Casey said, the biggest improvement is in handling. Mileage is too hard to tell, at best I'd say no more than . 5mpg. But, based on the handling improvements alone, I'd buy another. Trailer seems to handle better even in crosswinds, and it does well to keep the face of the trailer cleaner. Adjustment of the wing angle in critical, and Taylor has gone through some revisions in their mounts, the latest one is pretty nice.
And Casey, Yes- Taylor makes them for the sprint cars, which is originally where they started with them.
Kev