i have them on my 2001 sc2 they are alright they will only drop about 3 inch instead of the 4 that is advertised but they serve the purpose on my car for now
I don't have any experience with the HP ones, but if anyone wants I've got a set of Arospeeds that I used for awhile and liked that you can have for $75 + S&H *end shameless plug*. Keep in mind that a coilover will have a harsher ride than progressive-rate springs. If you want a stiff suspension that handles better than stock and are willing to deal with some jouncing and bouncing then they are great.