After seeing it used on youtube I bought two of them and my experience is that they are not a perfect replacement for just foam. The good thing is that the bass does not go as sharp as it does with foam. So it's possible to switch to the Fump on the fly without retuning. But I have to get the Fump as close to the saddles as possible to prevent rattling. For two of my basses with Badass bridges I had to file down one side of the Fump to be able to slide it in between the strings and the bridge.. On my B to G 5 string J bass it only stopped rattling when I slid the Fump in from the bottom.That works fine. I have another 5 string J bass strung E to C 100 to 30 light strings . On that bass the Fump did not work at all. On my P bass it works pretty well, but my action is low and the bottom side of the Fump needed to be filed down a lot to fit onto the Badass bridge. I also had to mess with the tension screw. I'm not sure if the Fump is meant to slide in from the top or the bottom. I think it works better from the bottom.