So not to be stupid but from looking at the description, this isn't the actual down-pipe, it says this will hook up to the factory down-pipe and they will be releasing one soon. Am I wrong?
no mention of the grade of metal used which can reflect on price + being flanged is a plus because anything less than 300 series stainless will rust or corrode fast if it was a slip fit. the downpipe is said to be the most important piece for quicker spool of the turbo, but of course less restriction after it surely helps!!
no cat = a code always + even bigger hi flow cats will sometimes do the same. the cat-s along with too many mufflers + resonators restrict performance in any turbo'd engine. factory pipes are for quiet to meet government specs for sure.
Cats are an advantage to every living soul that breathes air. Even though burning carbon-rich fuel pollutes the air, using cats helps reduce that by a significant degree. Removing them is tantamount to refusing to take kidney medicine because you object to it, and yet you'll die without it. The only thing is that cats don't affect just the car they came off of, they allow for more pollutants into the air that we all breathe.
Mufflers are needed to keep the rest of the world's population from being offended by loud exhaust noises. There are mufflers that do their jobs better by restricting the flow less, but they cost more.
Resonators are usually just large empty tubes that are sized to overcome a droning noise. Refer to the research by Helmholtz on resonant frequencies. You may know it better by how a Coke bottle sounds when you blow across the top of it, and how the pitch varies depending on the size of the bottle and how full it is. Resonators don't normally reduce the flow by any appreciable amount while providing a decided advantage for the occupants of the vehicle.
If anyone wants performance, they shouldn't buy a mid-level consumer vehicle. Go pay $$$ for a mid-engine sports car.