You don't get feedback from a PLB it is distinctly one way. It's even difficult to test the new 400mhz beacons.

Advantages: smaller lighter (with the new unit, cheaper) than a sat phone, simple to operate - just one button, also sends your location, battery life, since it is only used once you don't have to worry about keeping battery charged, generally more rugged/survivable.

Disadvantages - as you point out, it's press a button and hope. You can't summon none emergency help or ask questions.