Ive just looked those up and they are very very keenly priced, and let me explain why.
if you look at the pictures of these systems under the car (ie actually mounted) You will notice that factory bracing has been removed and the exhaust hangs lower than all other points on the car, almost in mid air, this is so that they do not have to have mandrel bends that delicately snake around suspension and diff.
So firstly, the stock braces if you have them will need removing, also the exhaust is now the lowest point on the car, so you will scrape through it very fast and it is likely to get caught pretty easy.
This is a stock system, see how it has braces (arrows point) and around the diff has quite a few bends to clear everything and its tucked up nicely out of the way.

Compare to this
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Also if you check their other products made with the same materials and with the same processes you will find these guys

these are known to crack at the welds and flanges and generally last under 6 months, remember this is the same steel and the same welding that holds together the exhaust systems you are considering.
So consider this before you spend the 5-600 dollars.
And also obviously there will be zero performance improvement from these catback only systems.
Dann