It doesn't sit well on the bridge, making the strings vibrate weirdly. On my violin, at least, it doesn't stay at all, only if I hold it with my hand and press it a little does it create the desired effect, but unfortunately, it's almost impossible for me to practice with it...
It significantly reduces the sound intensity. However, it remains sufficiently 'clean'. For those who want to practice but live in an apartment, it's surprisingly effective. I had to sand down the callus a bit, but it's barely noticeable. I recommend it!
