Just like anything else, done correctly
, this method is a very effective "hands-off" method of teaching a horse to give to the bit each way.
I use this method myself...though never in a curb bit as was posted in that link. I also don't "tie" the horse around. I take a single wrap around the saddle horn that gives enough resistance to teach the horse to give, but they can get loose in an emergency. I also never leave the horse alone. I am always within sight or earshot of the horse that's tied around.
There is also a "sweet spot" that is ideal for this method. Tie their head any farther to the side and they learn to lean or they panic and flip over. Tie it any looser and they don't learn to give the way they should.
The only reason I use this method (and I really don't much anymore because I've got more time now) is that it allowed me to do other things like ride another horse or get started on chores while the horse was learning.
It's not something that happens for hours (or at least it shouldn't
, even the most well-mannered horse would get tired and lock up by then), but maybe 10-15 minutes on average. Sometimes it only takes 5, sometimes it takes more, depending on the horse.