As long as the situation starts with a diver being only low on gas and notices it in time, gas sharing can be done calm and easily with any method.
I see the advantage of the usual octopus setup for the majority of occasional vacation divers with little experience. Every group member knows that the guide and each of his groupmates has a yellow spare regulator that he can grab anytime without endangering his buddy, and where to find it. The equally inexperienced gas donor likes to have a spare reg that he can donate, without having to switch his/her main regulator in a sudden stressful situation. They like this setup.
If an experienced instructor tells you how a student once stole a regulator from his mouth and how that was no problem at all because he just switched to his backup, that doesn't mean much. Stealing an infrequent vacation diver's regulator won't end well no matter how easily a cave instructor can handle it.
I see the advantage of the usual octopus setup for the majority of occasional vacation divers with little experience. Every group member knows that the guide and each of his groupmates has a yellow spare regulator that he can grab anytime without endangering his buddy, and where to find it. The equally inexperienced gas donor likes to have a spare reg that he can donate, without having to switch his/her main regulator in a sudden stressful situation. They like this setup.
If an experienced instructor tells you how a student once stole a regulator from his mouth and how that was no problem at all because he just switched to his backup, that doesn't mean much. Stealing an infrequent vacation diver's regulator won't end well no matter how easily a cave instructor can handle it.