Mike, and others....
Almost two years ago, when I ordered my 'Air Propagators', the larger size was not an option, or, available. The smaller, original size is good for stems up to about 3/4" diameter or thinner. Any stems larger than this diameter will need the larger propagators.
While the ball shaped, rooting chamber has a limited amount of space for the actual rooting medium, moss, etc. it was perfectly adequate for its intended use, i.e. to quickly air-layer a stem, and then continue to grow the new rooted plant in a larger container. Air-layers started in Spring will have the majority of the growing season to re-establish, and continue to grow in a new location, or container.
My step by step description took me longer to write, and post, than actually using the "Air Propagator". Bottles, aluminum foil, plastic boxes, all work, but the "Air Propagators" are amazingly quick and easy to put into use. That's why I bought a set. I hate work, and the "A-P" are convenient. You could set up 6 air-layers in the time it takes to prepare a soda bottle, plastic box, etc. Like I said, all the other methods will work just fine, but I like the convenience factor.
The best part comes when the ball is filled with delicate roots. You just open the "A-P" like a book, and gently lift out the rooted mass. Then, just simply, slip the new packed, root-ball into a prepared container, and watch your new tree grow. Unless you rip up the new roots from rough handling, there should be no set-back when your new tree is severed from the original plant.
I also use a thin, bamboo-skewer "cheater stick" to check the rooting area within the ball, for adequate moisture.
Good luck.
Frank