My last job on a 1920s house with those thin clay liners finally convinced me. I used a steel brush for years, always holding my breath. The poly brush just glides through without that awful scraping sound. It feels less like you're fighting the flue the whole time. I won't go back to metal for anything old or fragile now.

Yeah, that "feel it out" part is key. The book doesn't know your specific tree.

My T450 screen swap took five different panels, lmao.