RE: Ofna PBS/PCR Diff ?
You do not have to have 1. You get them on ebay for cheap. Any hop-up you want. Just do a search for "hyper 7" on ebay and you will see loads.
I ran with them and you do see a difference in better handling in the corners. On my 9.5 I have front and rear. I think it helps. But you do not have to use them if you like it how it is.