Biggest waste of money since dangly bits of rubber attached to rear bumpers were invented.
My parents had one once and I still decorated the back of my mum’s hair with recycled Sunday roast quite regularly.
Add a tuning box to a GTD and you’ll have something to smile about.
Add an oily filter and all you’ve got is an excuse by VW to wag a finger at you about warranties.
Seriously they do nothing unless you have a lot of other tuning going on. Diesels suck a lot of air so just cleaning your air box out once in a while and banging anything loose from your paper filter will keep it running just fine.