Very little to add to this. Exhaust is on and I've driven the car about 500 miles since, including 400 miles on yesterday's mid-Wales run.
I am very pleased - sounds throaty under acceleration and quiet everywhere else. No resonances apparent anywhere in the speed range, so it's unobtrusive on a cruise.
A small note on fitting. Rich did advise me that I would need to cut off the bracket on the air control tube. I wasn't keen to do this, as it's an eye-wateringly expensive piece (think £800+) and I wanted to do nothing to the car that was not easily reversible. I found that the bolts Rich uses for the back box straps are long and these prevented the air control tube from sitting where it needed to be. Some shorter stainless bolts solved this problem completely and I was able to simply use the longer of the two OE silencer straps, with a little bit of re-shaping, to secure the air control tube. All good