Gimmicks are short cuts. Using a tie down, martingale, etc in an effort to ONLY lower the head does not teach the horse anything expect to brace.
I have a horse in training right now that has come so far in just a few short weeks. Lots of ground trot pole and cavelitti work. She reaches and stretches on her own now.
Yes, side reins, etc would place her head where I want it but it won't build the muscle for her to carry it there for any length of time.
I always get a kick out the riders at shows who warm up with gimmicks but have to take them off for the class. Mid way in the class - UP goes the head.