in my experience with a previous car, they are good systems the garage i went to in swindon the blokes were a bit funny if you watched them but at the end of the day if im paying for something i want to make sure its how i want it.
i have also used longlife in bristol and found them alot better. the thing with power flow is they have 3 catagories for sound which is quiet or loud. where as when i used longlife they ask alot more and are glad to cut your bumpers if needed where as powerflow wouldnt touch mine.
you never know though mate you might get the complete opposite.
(remember these were previous cars not my toledo)