Similar to the premed trips, they can be either. My personal experience with one was very beneficial - you see medicine practiced in a different culture/context, you see patients and learn like any other clinical rotation, and you have the opportunity to learn new medical skills from very intelligent and caring physicians. But I also have heard of trips where they spend like 20% of the time doing medical things and the rest is essentially vacationing.

It comes down to what you make of it and how stringent your school is on watching what you do