A $9 brush doing the same job as a $40 one isn't some big discovery, it just means the expensive brush was overpriced. Half of those fancy tools are marketing anyway, the bristles do the same thing no matter what color the handle is. What actually matters is your sectioning and how tight you pull the foil, not the brand on the brush. I've seen people with cheap tools get better results than folks with a whole kit because they know what they're doing. So was the $40 brush really better, or did you just assume it was because it cost more?