Update: switched from a round wire brush to flat wire brushes and I was wrong to doubt them
I ran round poly brushes on every flue for 11 years and figured flat wire was just for stubborn creosote on masonry. Then a sweep in Rochester showed me his setup on a 8x12 clay liner with stage 2 buildup and he was done in 20 minutes while I would have been there an hour. Flat wire gets into the corners where the round brush just spins past, and the finish on the tile was way cleaner. Last week I did my first full day with flat wire only and the soot pile told the story. Anybody else made the swap, or am I late to this party?