There was some very faint turbo whistle. But you could only hear it at very low speed with the windows down driving next to a wall, ha.
It won't hurt air flow for sure but any gains would barely be measurable. It doesn't take much energy to create high pitched noise so there won't be much energy absorbed by the muffler.
Your car will have a different turbo so you may well get some noise. I just couldn't believe VW went to the trouble of designing and manufacturing a muffler for the 2.0 TDI engine when you can barely hear it without anyway. Especially when companies like Volvo or Mercedes don't seem bothered about the really loud turbo whistles a lot of their cars make.