The real problem here might not be the brush material at all, it's that the homeowner is comparing two totally different eras of chimney work. His dad was probably sweeping open fireplaces and old brick flues where steel wire was fine because the masonry could take the abuse, but modern liner systems have thinner walls and that same steel brush can chew right through them over time. So you're not babying the flue, you're matching the tool to what's actually in the house now. For heavy creosote on a liner I keep a poly brush with stiffer bristles around, but the brush matters way less than doing a proper chemical treatment first when the buildup is bad.

That "fizzy tang" line got me because I know that smell exactly. I brewed beer for about a year after a buddy told me my first batch was amazing, and I mean I went all in. Built a kegerator out of a mini fridge, printed labels with my dog's face on them, the whole thing. Problem was I only ever had like four friends who actually drank it, so I had kegs sitting in my garage getting warm and flat while I kept brewing anyway. Ended up dumping probably 15 gallons one weekend and my neighbor asked if everything was ok because he heard me swearing. The urge to keep making the thing after the crowd walks off is real.