I saw more like 7 RWHP. I have no idea about MPG. I usually see 4-6 mpg. I noticed a much lower temp in the pits even on a fast cool down lap. To me the main thing I liked was that the pump runs at full GPM even with the car sitting cooling off.
I've heard mixed reviews myself. Most guys don't recommend it for a daily driver. A few have even stated theirs failed on them and they didn't know it until the steam was pouring out from under their hood.