IMO, definitely go the name branded one.
The quality with the exhaust shop one will just not be there. Sure, it's one thing cutting up some bends, welding on bits of straight, bunging on a muffler or two. That'll make the exhaust come out of the back of the car, sure. But will it sound like shit and rust out in 12 months?
Imagine the design work that blitz put into the exhaust - they'renot a one of job, they're designed to be produced in numbers, so more expense can be put into the design. When you look at the exhaust, it looks like a piece of craftsmanship. They look so nice that you don't even want to put it onto your car, because it'll get dirty.