I am using this contact microphone for experimental music applications, with great satisfaction.
It is obviously designed for the bell of a wind instrument, and as such, mounting options on various surfaces are limited.
An impedance adaptor (DI/preamp) is absolutely necessary to get a usable, full sound out of it. I am using the TritonAudio BigAmp Piezo, which works perfectly well for this purpose.
The frequency response can be very dull depending on placement. I've had great results using the back of the microphone (where the "Korg" brand is printed) as a contact surface: it's much more sensitive to high frequency content, most likely because of the hard plastic's rigidity.
The cable and the strain relief at the microphone end feel flimsy and durability may be a concern. At this price, it wouldn't be a big deal to replace it! Very much worth the price.