I have powerflex on my ser 3 16v
They don't do the ARB, superflex do
SuperFlex: Advanced polyurethane suspension bushes
I would start with the rear, 8 of the same type then 2 on the panhard rod.
If you can get hold of some old link arms and get the old bushes pressed out / burned out then the powerflex ones are in 2 pieces and will be easy to do yourself or use a vice to press them in, then swap them over.
I would advise using large washers x16 +4 for the panhard rod, either side of the bushes.
I was put off in the same way as you, people saying cars squeaked ect ect but I have had no problems in that area.
When doing the fronts you will need 7mm spacers, I used 4x 3mm spacers, unless powerflex has changed their design, see my thread on it
IMO a well worth upgrade, car turns in sharp and settles on the exit of a turn far quicker than OEM, NOS bushes not as good