Great at idle, but grating after that. I had a 2.5" Delta 40 or 50 on mine, and I stopped driving the VX so much because it was so loud and awful inside - it felt like the muffler was piped into the cargo area. Don't do it.
I replaced it with a 2.5" Dynomax super turbo muffler late last year and have been absolutely ecstatic with the results. Similar burble at idle, but far better sound quality and far lower sound level than the FM.
Crotchrocket, can you get Dynomax in UK?
Good luck all!