While one may get the air pruning benefit with all fabric pots I have tried several fabric pots and have not found one that achieves the same anchoring into the pot as I get with the SPs.
The smart pot is the only brand where I've experienced roots actually growing through the pot and being air-pruned on the outside. The roots actually anchor into the fabric to prevent root circling, spin-off, etc.
The Roots Organic Root Pot, Hydrofarm Dirt Bag, along with another fabric bag which I think comes from CAP or Hydrotek did not achieve the same. I may have possibly still received the benefits of air pruning, but in all of the pots mentioned above I was able to slip my hand down between my root ball and the fabric bag. Could not achieve the anchoring/ porcupine action like I got with the Smart Pots.
For whatever its worth.
I like those roots anchoring into the pot, getting caught up in the fabric..thus signalling to the plant to send out another, and another, and so on. Maybe its physiological, but I didnt like seeing my root ball sit loosely in the no name pots..almost as if my root ball had shrunk away from the sidewalls of the pot.
I've had the exact same experience with the above, smart pots vs. Roots Organic pots. Didn't seem to affect yield but seeing the big roots coming out the bottom is always reassuring.