I opted for the K-tec silenced one, because my K-tec exhaust was already loud enough. The quality seems good, marginally louder and I now get nice bubbling sound under deceleration.......oh although the power gain is relatively small, it is definitely noticable.
As for the K-tec and BB Tuning ones, well, theyre just straight bits of pipe so are going to be very similar i would have thought.
Get the silenced one if you dont want your exhaust much louder