This pickup is designed to fit underneath two of the feet on a guitar bridge. I tried this and didn't like it at all. I took it off, removed the resonator and used Everbuild Mammoth Powergrip Double-Sided Tape (A hearty product plug for a superb and essential product) to stick it to the skin underneath the bridge feet. Now it sounds good and works well. The piezo pickups are small and don't show through the skin.
I don't usually chuck in gratuitous plugs, but every guitarist should own a roll of Powergrip double sided tape. You have been told.