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When you say "down pipes", you are removing the primary cats closest to the headers?
That will trigger a check engine light (tune will resolve) and will smell really bad.
Note: Are you keeping your secondary cats or do you have a straight pipe there too?
Experience share: My secondary cats went out so I gutted them out, big mistake. Car smelled like *****.
Couldn't find OEM secondary cats so went with Magnaflow.
That smell is a matter of preference. However, professional installation in a good tune should have no effect on reliability, any increased wear would be due to harder driving since you'd be more incentivize because of the sound.