I could't follow the link but if you are referring to the rear subframe bushings, I would consider that stage 2 or 3 of the suspension upgrade. The job is pretty time consuming since you have to drop the rear subframe. In order to do this, you'll likely need a lift, and a transmission jack. It also requires the removal of the rear brake lines so you will need to bleed the brakes after everything is put back together. Indy shops in the US usually charge between $600-800 in labor for the job. If you are seriously looking to improve the handling characteristics of the car, this mod is well worth the time and money. Prior to replacing the stock bushings with M3 bushings, the predictability of the rear end was always in question. Any off-camber corner, or a corner with a crest or bump that unweights the rear end would completely upset the car. It almost felt like four-wheel steering would kick in at the worst possible moment. All that being said, I probably wouldn't go through the trouble of replacing the bushings until you're ready to move to a stiffer spring/damper setup or add camber plates up front (both of which will exaggerate the rubbery feeling of the stock bushings). Just see how you like the non-RFTs first and attack any concerns one by one starting with the simplest fix.