Dropped $180 on a rotary chimney brush kit that ate my own flue liner

I'm still kicking myself over this one. Last month I grabbed a rotary brush kit off a supply site because I wanted to speed up the hard creosote jobs, and I figured it would pay for itself in a few weeks. First real run was on a clay liner out in a house off Route 9, and it chewed a groove right into the tile inside 20 minutes. The homeowner heard the change in pitch before I did and came out asking what was wrong. I ended up knocking $400 off the job to keep her from calling anyone else, plus the kit sat in my van for a week. I went back to my old flat brush on rods for the rest of that month. Has anyone else had a rotary setup bite into clay tile like that, or did I just get a bad arbor head?