Just installed the Akrapovic SlipOn. The look is amazing!
The sound isn't a lot louder than stock as expected. It's deeper. The popping/burps are actually a little louder on the stock.
I did the same upgrade with my last bike VFR800F. That Akra slipon got a deeper than stock. And after a while the sound after got even deeper.
Wonder if anything changes on this slipon after some usage. Guess time will show.
Anyway, I think it's expensive but I really like how the bike looks with this slipon. (got a deal and paid 922$)
Made a video. Just remember the sound is from a GoPro camera so the quality is just ok.