Mine lasted for a coupel weeks, infact I still have some, If you are doing a big job ,I usualy used one set, I used to use 1″ in a bat. drill to cleane from 1-1/4″ up.
The key to using a fitting brush is to turn it one way only. The brush will last far longer if you use it this way which is actually the proper way to use a fitting brush. Cranking it in both directions causes wear and fatigue breakage of the steel bristles.
I have found the Milrose brand brushes to be of top quality and very durable.