It's cheap, it lasts for years, and it's the quickest way to clean cassettes, chainrings, and derailleur pulleys.
This brush is the best at what it does. It's shaped perfectly to reach into the nooks and crannies of cassettes. It's durable - I haven't worn one out yet at home. The scraping end fits in between the cogs of a cassette and is great at busting up thick, caked-on grime, and the brush gets everything sparkling clean again. What more could you want from a five-dollar tool? Whether in the shop or at home, this is my go-to tool for a dirty cassette.