I only flew one 5 day trip to Sao Paulo with a 3 pilot crew and it was only the fact the two FO's were outstanding pilots that made me feel comfortable taking my break.
Once in a while I felt I could not leave the cockpit for a Lav break so made sure it wasn't required because I didn't trust the other guy to handle a problem. I probably wouldn't have left the cockpit with these two guys flying. Neither one seemed qualified to be doing their job.