Rootbound is a pain, well root issues in general are, because root issues can look like any of the nutrient issues listed above, and most likely will make your plant look like it’s suffering from more than one. Soil users will need to watch for rootbound more than they would with other growing mediums, and remember the guideline of 2 gallons of soil for every 12 inches of plant height.
You can also only confirm root bound by pulling out the plant from the grow medium. Yes, I said that right, because almost all of the soil will stay attached to the roots as a big soil root ball when you pull the plant out.
When growing with coco coir in a fabric pot, I can feel the outside fabric container and top of the coco coir and tell when the roots have gotten to the edges heavily.