i got this fitted from same seller , you will have to knock the hangers down slightly if you want it to fit snug to the bumper. The tailpipe alignment on mine is also good. I have the mid pipe fitted too, also the y pipe to go on.
You wont notice much difference in sound with just the box fitted, and may struggle seperating the midpipe from the back box
many remove midpipe and back box together due to corrosion !