Same old shit, POWERFLEX are dearer NOT better.
POLY is POLY is POLY.
It is a liquid that arrives in 105 gallon drums(or smaller) that you mix with dyes, elasticisers etc, then pour into a mould, let set sell bush.
POLY can be bought in many grades, ie SHORE which is the hardness scale, the higher the number the harder.
Having used DEFLEX for years, and after I had used powerflex, I find NO DIFFERENCE IN QUALITY only PRICE.
DEFLEX make bushes for desert racers, which do not fail so if they don't they are even less likely to on a road car.
IMO powerflex are a rip off, the stuff is easy to use, you could buy it and DIY if you wanted as the moulds can be made from pretty much anything, ie MDF, wood, plastic, resin.
tabetha