I just did the same swap the other day, and what a massive difference. Nice throaty, mean sound. The popping on deceleration is definitely a lot louder, so I'm going to have to check for leaks (though I was pretty diligent when installing, so think it may just be something to get used to). I'll have to try to fab up something to allow me to record it when riding so I can post a video.
I definitely wish the new exhaust would have come with a new exhaust gasket. It's REALLY easy for the original one to come apart when removing the clamp from the old exhaust to the header. I ended up trekking to the Triumph dealer to get a couple of new gaskets (so I'd have an extra). At $11 for the gasket, it should have been included.
That third bolt was a challenge to find for sure, until I took off the other two and wiggled it around to see where else it was held up. That stock exhaust weighs a ton. The other thing I'd note is that if you have a GT (our have converted your R to forward controls), there is no need to remove the heel guard, since it's not in the way. The instructions also mention removing and saving the bushing from the center exhaust mount location (the one that's hard to find). You also need to do the same with the left side bushing, as the only bushings/bolts you'll reuse are the ones on the right side. I'd also recommend putting some black nail polish on the scratched part where the left side bushing mounts, so that it doesn't rust (it doesn't look like that existing bracket can be easily removed unless I'm missing something).
Other than having to search for that third bolt and get a new gasket, total install time would be pretty brief (i.e., on the order of 1/2 hour of actual work).
Overall, probably the most significant change I've made to the bike since I got it about a month ago. Killer sound (though the decel popping is a bit more annoying than pre-swap).
B