John, I have done a couple of stairs on a flat weave, it was a runner type stair carpet.
It had a kind of checkered or tartan pattern, it was blues and whites.
It was only to get up a specific stain which came up really well, I do remember thinking I would not like to clean it all when it get properly soiled. I had this feeling ground in soil would not come out easily.
I used a 6 inch stair tool and my Truck mount. No stain removers or prespray. Just hot water. And only a couple of quick passes, it was fine with that. But at your own risk

Craig