the bushes wont really effect the ride quality on these too much in the way you think, its more down to your suspension working properly and your tyres being inflated and right size etc which will give you the correct ride, powerflex or the slightly cheaper flo-flex will do the job and both will more than likely outlive the car anyway, takes about 30 mins in a average garage thats if they know what they are doing

when I got my zs as a daily the previous owners garage did this which was just criminal for how much these things cost (rammed in tyres valves ) and this was the better of the two