powerflex are semi solid suspension bushes.
Bascially the more solid the bushes, the firmer the ride and more direct the steering is. Cabin vibration is increased.
In my opinion powerflex bushes are really good medium between driveability with stiffening up of the suspension and slight increased in cabin vibration. Have used them in my old saxo through out the car
normal car bushes are a hardened rubber, then next up is varieties poly, Nylon bushes which are slightly harder and then theres alloy which is only for hardcore rally/race cars as it undoes bolts with the vibrations.