If a catless downpipe is not triggering the check engine light, it's because it comes with an O2 defouler (mini cat)
If that's your route, you can use the same solution with any brand—no need to get the more expensive ones.
I would not get either one; you'll never use it.
It already comes with stock O2 sensor bungs which is all you need.
BTW Evolution Racewerk's quality is second to none, it's one of the very few companies that still make their products in the US
The engine will run smoothly without any custom tuning. You cannot custom-tune Dinan.
Depending on your mods, you can get up to 25 whp from the downpipe; with your current Dinan setup, you'll probably get 15 whp since you cannot run a stage 2 map.
The highest quality pipe is the evolution racewerks. It's handbuilt in the US. Best finish, wielding, etc..
Many brands are proven to fit without issues, Evolution Racewerks, Active Autowerke, MAD, etc...
If you get a proven brand, it'll be 304 stainless steel. The cheaper eBay ones use the...
HUndreds of these downpipes have been sold and tested. No Check Engine
if you get a check engine light, active autowerke will replace the downpipe for free
If thats not a guarantee then i do not know what is