On his dyno, it didn't show any negative effects on his low end. Although, being an Auto you cannot see below the 3k range. It did pick up a lot as the RPMs increased though. A significant amount. For N/A, headers and Y pipe with stock sized catback is a great combination to keep the scavenging velocity up.
Once a larger catback is installed, that is when it really shifts the torque curve. That is when more power out of the engine is necessary to take advantage of the added flow capacity, and bring it back forward.
I promise you, his headers, URD Y, plus TRD Gen1, larger T.B., and X-1 has plenty of low end tq. Plenty.
Also, by the routing which is clearly visible in Super Werty's pictures, it routes the exhaust away from the U-joints. No cooking.
It does route it under the trans, so depending on how rough one is off-road, a strong skid might be needed to protect that area. I am reminded of Colinb's transmission skid right now. Crazy heavy blasted cut me. Lol.