The springs are non-progressive -- progressive springs vary their firmness depending on chassis load -- more at heavier load.

This means there is no variation in spring firmness under light chassis load. Put another way, they are as firm going through a parking lot as they are on a race track.

In spirited driving, they are adequate, though not excellent, and in daily driving are better than the regular Z, but quite harsh and jarring over even light bumps (cobblestone roads, speed bumps and the like, can be grueling).

The major advantage is that they are better than OEM for performance, but IMO, are a bit unpleasant for every day driving, relative to the regular Z springs or to a nice sporty progressively wound set, like, say, the Swift R's.