Not sure what Powerflex claims, but I have read in Roundel that the urethane bushings don't last as long as OEM on the streets due to road conditions. Apparently, they are great for track use where the pavement is smooth, but potholes and bumps don't seem to agree with the urethane ones.
Side note, I just saw that there was a massive fire at their UK warehouse/factory.
Powerflex