The double colander technique, to my knowledge, was first described in Kindai Bonsai, reprinted in the Kindai Bonsai "Black Pine Special", translated and printed in Bonsai Today, and again in the Stone Lantern "Pines" book. The first season the tree grows in the single colander. Then it is up-potted, colander and all into a larger colander. The advantage, as you say, is air pruning, but also the ability to water and fertilize more aggressively. With the second colander the advantage is continued growth in a larger container, without the full disturbance of repotting. I also feels it gives an extra layer of insulation during it's first winter in the colander(s).
It was suggested to me, that in ground growing would benefit with the use of some kind of grow bags to contain the roots. I have not attempted that, but do have some things in the ground in my mother's flower bed.
If you're interested in JBP I would highly recommend the Kindai Bonsai "Black Pine Special", if you can find it. If not, the Stone Lantern "Pines" book is an ok substitute, even if they do confuse the terms pinch, pluck, cut, decandle, needle, bud, and candle. (The "Juniper" book also has some of these same confusions, so be careful!)