I dont think that is root bound at all.
Mycorrhiza is in Promix!! a soillles commercial mix.
I have had out door that veged for two months grow out of one on those.. It was 6 ft tall and i put it in the dirt 2 weeks after flowering... You think that is root bound? no way!
If it is just cut holes in the bottom and let the roots grow into a differnt bucket.
Actually Micorrhiza is a micro organism, a type of root fungus. It helps your roots grow bigger, faster, and it helps them colonize better and absorb more of everything.
To illustrate, I transplanted the first two on 1-6 and the other five on 1-13 and I transferred them from 5gal to 10gal containers. I just took them out to treat them for mites and ripped the newspaper at one of the drain holes, and the roots are already there. Now that's fast!
As you can see in the pics, they weren't really root bound yet, but I wasn't going to wait till they were because I'm not advanced enough to cut the root ball yet. I still have a lot of research to do on it.
I'm sure they'll be root bound in the 10gal containers before I can harvest, but I'm out of room in the walk in closet so they're stuck in the 10gal containers. I'm hoping that after the roots run out of space the plants will redirect that energy to the part of the plant that's above ground, and I'm hoping not to see any bad side effects from being root bound. But only time will tell.
Also, the MYKEs may not have done it alone, I also have them in FF soil that has Mycorrhiza of it's own. I'm not sure if it was the MYKEs or a combination of the FF & the MYKEs. I'll be doing some experimenting on future grows to see. So stay tuned root fans.
My plants are between 21" & 28" even though I've had several problems that slowed the folliage growth, and they've already sucked all the nutes out of the FFHF that I used to transplant into the bigger pots. I just lost a lot of leaves last night to nute deficiencies and I fed them today. There doesn't seem to be anyone I can turn to for advice, so I'm learning how to take care of plants with monster roots. If you try this all I can say is keep an eye on them and feed them when they ask for food. And expect them to ask for a lot of food. lol
By the way, fish emulsion fert is naaaaaaaaaaasty stuff.