|coilovers since the spring rates are the same, 8K front & 6k rear. They both use a type of rubber in the top mount as well.
The FlexZ doesn't use pillowball upper mounts like the Flex or MonoFlex. That is the change that makes it more comfortable/streetable. I'm not sure what Tein has changed in the damper itself.
These spring rates will be too stiff for most though since they are way stiffer than stock. The weight of the car will have to overcome that spring rate before the spring even compresses and I think that is the stiffness most people refer to.