I do not use stud chains on the Minis. For that matter I never used stud chains on the Morgans, even for breeding. I always used show halters, not bridles, for showing our Morgans, and on some horses--one stallion and a couple headstrong geldings, I would use the show chain over the nose--I'd run it through the far ring, over the nose with one turn over the halter noseband to keep the chain in place, through the near ring & then snap it to its own ring under the chin--making a loop right around the horse's nose--it gave more control than just a plain halter, but didn't apply the force of a chain snapped to the far ring & run across the nose, nor did it have the force of a chain under the chin, run through both rings and snapped back to itself, so that it squeezes tight when you put pressure on the lead. t was mild yet effective
On the minis I've had no reason to use a chain. Even when I bought an unhandled, unmannerly 2 year old stallion--a good sized B--I did not have to resort to a chain to teach him his manners. I just can't imagine having to use a stud chain on any of the smaller ones, unless I were to get one in that was older and has a history of misuse of a stud chain--then I could see him being set in his ways and oblivious to any restraint short of a stud chain...and yes, I have seen too many horses have chains overused on them, and that is why I cringe when I hear someone tell a novice to use a chain to teach manners to their horses.