Someone truly perfectionist (more than me apparently!) looked at that video in the web link you attached, and they found all sorts of flaws!!!

They said my horse was crooked and I should have fixed it up!!!

Considering we had only been long reining a month or just a bit more in that video, I was pretty pleased - guess I forgot to mention this fact to the person who was identifying the flaws!
I bought several long reining books (including the Stanier one) and found them either too advanced for a beginner, or a bit shy on information or quite disorganized in content. Good tidbits in all of them, but none of them became my bible of long reining. Have yet to find one...