I did this a few weeks ago. It was funny. I reached into my golf bag to pull out a random tee to use and just so happened to pick this one out. Very apt.
As for the mod itself, I didn't notice much difference to be honest. It is marginally louder at idle and low revs but not really all that noticeable. The biggest difference I experienced is that the car now burbles and pops when I lift off the throttle in any gear. It used to only happen in 1st and 2nd and occasionally third. It now consistently happens in 4th, 5th and 6th also. It's subtle but it's certainly there. My opinion - it's worth doing but don't expect significant results.