This is the thread you need....
https://z4-forum.com/forum/viewtopic.php?f=2&t=109995
Video clips start on page two. The first clip is a fair representation I'd say and I don't think my phone would capture the sound any better. I can try if you like though.
I've had one on for maybe six months and I love it. A much deeper, louder sound. I daily mine and it is a bit intrusive on longer motorway journeys but I don't do too many of those.
It does sit a little lower but mine is on eibach springs and still clears speed bumps okay.
Once I got the old exhaust studs drilled out it was a really easy fit. I recommend a few good cobolt drill bits!
Your welcome to come out for a spin in mine if you're anywhere near Dursley.