i would do the single exit option.
I've previously had a K-Tec exhaust, and now have a Pro-Speed the same as the one above...
my experience of the K-Tec was very good, it fitted perfect and the quality was good. There have been problems with fitting though, so if possible let David fit the K-tec one himself.
If i was choosing again i would go with Pro-Speed all day long, purely because of the fact that they're custom made on the car... so gauranteed to fit and you can choose exactly how it looks, none of the "off the shelf" exhausts that k-Tec sell.
Thats my 2p's worth after experiencing both K-Tec and Pro-Speed exhausts