I have a straight through powerflow custom one.
Benifits are:
Its custom made so it goes high over the axel, lowered it 100mm and it didnt bang.
Lifetime garantee, they will always fix it for free if it leaks etc
Good workmanship at the dealer i used (ipswich)
Sounds amazing
Unlocks restriction, possible BHP increase, and will help with future mods
Bad points:
Drones at 70mph due to their being no middle box's and silencers
Cost £350!
Has a hole where i parked it onto a curb and i cba to go get it fixed for FREE.
Hope that helps. I also had a sports cat fitted for and extra £200. Would recomend a Manifold too.
Worst part is, it will all be up for sale soon as i need a bigger bore for the VR engine to go in!