Insulated Chimney Liner vs Poured Concrete + Vermiculite

[TomasB]

That thin inner layer gets snagged when cleaning leading to a hot spot that makes it get worse

Does that inside layer more likely to snag when you use a spinning broom on a flexible shaft, or a regular one when cleaning with up/down motion?

I can see a spinner being a bit more safe, as long as certain rotation is maintained, that doesn't try to clip on those "gills" but rather follows the direction (which I will definitely need to take a note of that!)