To me a blocker tie ring teaches a horse that if it sets back enough the rope will slide thro. A horse will set back or panic if it feels trapped.
I think they're great, but do agree they can lead to this behaviour - left brained, calm pulling back - depending how they're used. Speaking from personal experience of the first horse I taught one with
IMO they're(or the principle behind them) a great help in *teaching* a horse to tie calmly because not coming up against unyielding pressure greatly reduces the fear of being trapped. But the trainer still needs to take an active role, take the slack, so they can ensure the pulling back also doesn't get reinforced & 'respecting' the pressure does. The horse still needs to learn to tie firm too & I don't see them as a replacement for general tying use(that'd get expensive too!), except in situations where it may not be safe to do so. I use Tie Rings in my trailer, and to tie places it's not safe to tie firm to, but I wouldn't leave a horse unsupervised on one unless already well trained... & there was a knot in the rope to prevent it sliding.
Those sierra halters look like they're a rope version of the old collar idea. I have nothing against using a collar, but not a thin, sharp one, especially if on a fearful horse. Maybe perhaps on a calm, left brained puller tho... as I can't see how it would possibly stop
a horse pulling, but it may be painful enough to dissuade a horse that's not reacting in panic. For the same reason I don't use a rope halter when first tying a horse solid - wide & flat reduces likelihood of injury, should the horse really fight it. The sierra thing could be used in conjunction with the tie ring principle, to teach a panicky horse without risk too tho.