I think the powerflex are fine except in the rear beam, where they don't have a big impact on handling, but do make things a lot harsher. Typically this is the one where they are easier to fit!
I have also heard that the poly ARB bushes can squeek, so when I changed my ARB I just used new Ford bushes.
I think the Ford bushes are a lot cheaper than the poly's, probably varies depending on application.
I have replaced all of mine with new OE bits, inc. the FRP uprated bushes, with the exception of the lower arm front bushes, when these go I will probably go for polys, but elsewhere I think the Ford bits are fine.