It's all very well doing that when you've got a spare engine, fully servicable and available on the other wing. It's the pucker factor when you know that the engine keeping you going is all you have left that counts.
We all know how reliable the engines are most of the time, so what were they trying to prove with this flight? IFSD rates are all very well but if the shutdown was because of something more serious than just a precaustion, say a mechanical failure of a high speed component, then so what if you can fly for over five hours on the other donk if there could be damage not only inside the bad engine itself but in the event of an uncontained failure what about damage to other systems and aircraft structure?