Used on some (non K&M) stands in order to counter balance my heavier mics.
Most mic clutches tend to give over time, and this counterweight is the ideal counter to that. I don't think you'll ever be able to perfectly balance with one, but they take a lot of the stress out of the central clutch rubber.
Simple to install too - remove anything from the mic stand's boom, slide this on, reassemble. Solid weight and can be used to settle arguments with drummers.