I have one and it's useful in the summer when I can go a month or more and the chain isn't really all that dirty, but in the winter when a single ride can leave the chain caked in gunk, they're basically useless. At those times, removing the chain and doing a long soak in a jar with mineral spirits, and maybe some hand scrubbing is the solution. If it's really dirty (like, actual dirt) I'll do a hot water and dish detergent in a jar and rattle it around round first, maybe 2 or 3 of them, until the water is at least semi transparent, then go to mineral spirits and soak for a few hours, shaking once in a while. Then wipe down with paper towels, dry and relube.