Firstly, my wood-heater chimney is straight up and down with a 30 degree pitch on the colorbond (metal) roof. My heater has a non-removeable internal plate, so I can only 'sweep' from the top.
My chimney sweep of choice = a steel star-picket (T-post, Y-post, etc...) with a few wraps of chicken wire (about a yard/metre long & a foot/30cm high) wired to the 'top' of the picket. There are handy holes in the picket to run the wire through to hold/tie the chicken wire onto the picket. If it's not wide enough, just add more wraps of chicken wire.
I then tie an appropriate length of rope (diameter to be able to thread through the picket's lowest 'hole' (towards the point).
I drop it down the chimney, chicken wire end first, and work the whole thing up & down the chimney. I do need to clean out the plate of the heater a few times during the operation so that I don't compact the 'sweepings'.
https://unitedhomeservices.com/chimney-sweep/dallas-tx/
The chimney is 'shiny clean' at the end... and I haven't had to spend $$$s on sweeping gadgets/brushes.