Breather Bags/Air Pruning
I'm looking at bringing on a few young trees for topiary and such like, but don't particularly want to put them in the ground in the short term. So I'm hoping for maximum vertical growth for a few years without doing too much to them. If I were to attempt to do this in typical pots this would take a long time and end up with pot-bound trees. However, I've been looking at alternatives like the Oregon Beather Grow Bags?
A. What do the experts make of these? Particularly arborculturalists.
B. Are there alternatives that people know of in the UK? Shipping from the US is quite pricey.