That's a "cat-back" exhuast then, which means you still have the three cats in place - uppipe, downpipe and the catpipe.
You can get rid of the 3rd cat for about £100 (Gus the bus can get you one, that's who I got mine from) and you don't have to worry about remapping then. Removing any of the other two you'll have to start looking at mapping. It would give you a wee bit more power and torque. My car made 248.5bhp and 232lb/ft of torque with 3rd cat removed, miltek centre section and H+S backbox.
BUT! I'd take the handling mods any day of the week. Droplinks fitted and prodrive geometery settings dialled in should cost you well under £200, and they are fantastic.