"This review is for the medium gain (red) version:
Simply put: these sound phenomenal. The top end is clear and the bass response is fantastic. Having used Shertler contact mics in the past, I can say definitively that the frequency response of the Marshmallow is much better, and without the high-end rolloff you get with many piezo contact mics. The build quality is great. The cable is a bit heavy, so care must be taken to position the mic and source before connecting to your preamp (if you've never worked with contact mics before, they are VERY sensitive to movement along the surface they're mounted to). I had great results connecting to a mic pre at no/low gain (line level), as well as a DI input (Rupert Neve Designs 517).
Michael is great, and extremely responsive. Shipping was fast, packing very good. A+++"
Metal Marshmallow II Piezo Disc Contact Mic And Preamp