I bought 2 extenders, j style and the universal one with the screen, they both work 100% . I decided to use the one with the screen since it is easier to install and remove. If you don't have a tune and want to eliminate the CEL caused by an aftermarket downpipe, then this is what you need.
Mk7 GTI stage 2 owner, I was in a pinch after getting rejected for inspection for emission. Ordered this, pointed it against the flow of the downpipe (pointing more towards the engine for reference) and well-ah. Flash back to stock, install this , I have a catted downpipe and used the biggest insert and it worked!