I think the point is a brush cannot be repaired, whereas if the spring breaks in a univalve it is a replaceable part, so throwing something away that can essentially be repaired for a part that would only cost a few pence goes against common sense. Just because a new univalve only costs a small amount of money doesn’t negate the fact that it can be repaired. If your car, washing machine, oven, boiler, etc break, you replace the broken part, you do not buy a new one, so throwing away a £30 item that I know can be fixed goes against the grain.