I have been using Tampermonkey for years. AFAIK, it is safe as long as you know which scripts you're importing. It's just easier than creating an extension for every script I use (I currently have 3 for the forum - enhanced merits, this one, and to quote posts on locked threads).
Unfortunately I'm not as familiar with technical stuff like coding and scripting as you're talking about, that's not my basic in the real world so I really have trouble with technical stuff like that. LOL
About of extensions, it looks like I've installed quite a few extensions at the moment like BPIP as well as a quick report to the mod. I haven't tried more, but it might be worth trying if in the future I need it. The extension has changed some of my current views when using forum. By the way, thanks for convincing me.