Kooks has had some quality problems of late- seen a few headers with gaps in the collector where the primaries are supposed to be welded together. PITA but Kooks took care of it right away. YMMV.
Since the speed shop I plan to use for the install stocks them at all times, that's probably not a concern. All they do are Mustangs so I'm guessing it'll be a pretty quick install/tune when I make the move.