Looks good Carlos except you have a gnarly mass of roots at the bottom that
may need trimming or at least untangling. If not you may get a girdling effect, which killed this Pickering recently. (That tree came directly out of an untreated PIN pot).
Like you have planted thousands of trees and grapevines by hand (about 10,000 Christmas trees and their replacements) both in pots but mainly in the field and I always try to insure that the roots grow out into native soil like spokes on a bicycle wheel. Think of the axle as the trunk and the roots as spokes radiating outwards. If they J root or girdle, the tree is toast.
Spin out mainly occurs at the bottom of the pot which you've witnessed.
Those roots should be touching the product, should be chemically pruned so that you get more of a diffused mass of roots. That is where I concentrate my application of the paint,
at the bottom of the pot, and it works. I don't mind the roots hitting the sides because they'll be diverted down to the bottom but once they reach the bottom I don't want any spin out (circling).
To get technical, when a root tip is terminated (killed), either by chemical means or air/light, you'll get a profusion of lateral roots approximately 4" from that point and behind on most plant material. That means that this system is only temporary and upcanning or planting into the field is necessary at some point in time.
I'm like you regarding potting mixes, whatever is on hand but I do stick with a 50/50 mix of inorganics and organics.