RE: are string leeches a loss rather than a gain?
Depends on where you put them on the string, just like any other silencer. I didn't lose anything when I used them. I just didn't like them because they didn't last long enough, and any rubber silencer I have used made a rubber whipping kind of noise. Still quiet mind you, but the yarn puff balls don't even do that. Not to mention they are cheaper and last a lot longer.
Paul