Advantages: (1) They can give you a very natural sound if positioned well; more natural, often, than either under-saddle piezo pickups or magnetic pickups. (2) They can be combined with other contact pickups and/or other types of pickups, to blend different tonal characteristics for a more natural "whole instrument" sound.

Disadvantages: (1) You need a preamp, which generally is not intrinsic to the unit; it has to be purchased separately, either for installation in the instrument (usually at the jack), or outboard. (2) They are very sensitive to position; move one a half-inch over and you might dramatically affect the tone. (3) They are prone to feedback in high-volume situations, which effectively makes them unworkable for me. (4) They pick up any sound from the body -- not only musical tones, but also incidental finger taps on the body, the sound of sleeves brushing across the face of the instrument, etc. -- which can be pretty distracting.

Definitely one of the options, and some of the new ones (like Pick Up The World) are getting pretty positive reviews. Good luck in your search.