The bungee is better than the pre-fabbed ones or the surgical tubing. The prefab ones are too lose at the mouth piece IMO. I bought one and threw it in my save a dive.
The way you make them with surgical tubing to take a length (whatever is comfortable) lap the ends. Use 2 zip ties so you end up with what looks like a pair of lips and slip your mouth piece between the lips.
With the bungee you kind of do the same to make the lips, but instead of zip ties, you make two knots. The knots will slip a little to tighten up the necklace around the mouth piece.
Here is Gombessa's method.
