I can comment on Two Bros, as my used FZ came with them. They did not have the db insert in them.
When I picked up the FZ, and rode it home, by the third stop light, I couldn't wait to shut the bike off. I had a headache in about ten minutes. And this is coming from someone who has hearing damage from too many metal concerts(and not wearing hearing protection), and blasting his car stereos. They have a loud, bass-y drone that gets old real fast. And it gets worse when you're cruising. Best example, is either a Mustang(any year) or a Suburban with those straight through Flowmasters or equivalent. I'm sure you've seen/heard both. You know that loud, hollow bass drone? That's what these did. I ordered up a set of the P1X inserts, and now I'm happy. They're still loud, but not piss-of-your-street loud. The inserts took away all the annoying drone, and got rid of most of the bass, but there's still just enough that it sounds great. They also gave the bike more of an F1 car type scream when accelerating hard. I love the way they sound now, even if they are still a little bit too loud.
My cans are the carbon fiber, and they have turned yellow, despite my best efforts. Something to keep in mind, is that CF will turn yellow, unless you repack them EARLY, and lather on some 303 protectant on a regular basis. I repacked them on Saturday, and that was NOT fun. The packing in them wasn't even burned out, but they still yellowed from what little got through the packing. The Scorpions, do not need to be repacked. This is something to consider. If I don't have new cans by the time these need to be repacked, I'm going to just pay someone to do. I'd rather tear the engine all the way down and rebuild it for the heck of it rather than repack cans. lol Also keep in mind, only the CF and Titanium cans have to be repacked sooner than the aluminum cans.
Really it comes down to your preference as to how an exhaust looks and sounds. I like a bit quieter, and no maintenance. Others want it as loud as possible while still having mufflers, and maintenance is no biggie. Honestly, I'd love to keep my Two Bros, as I LOVE the way they sound(with inserts), but I'm too lazy for this repacking crap.