One advantage is that they don't need a pre-amp, so these could be connected directly to an ADC or a port pin on a micro with built in ADC so there's fewer places to pick up noise in the signal. Also their internal circuitry filters out noise from the power supply lines.
For directionality I think there's a few methods from putting the mic in a tube to using two on opposite sides of a large plexi sheet; can't remember the specific details off head now, but google will help you there :)
Haven't tried them myself yet tho so I can't say about the quality, but I'd assume they're good since there is so much emphasis on minimizing signal noise.