JustDressageIt - that 2nd vid is a wonderful example of a false frame. The horse is tight in their throatlatch, lacking the relaxtion to truly stretch and reach and engage the hind end, and is disconnecting energy just behind the withers. The hind is tracking up but the energy stops there as the horse braces their neck and jaw. This results in the horse slightly behind the bit, the lack of full range of shoulder motion, and the misperception that the horse (who may be clipping their front with their hind) is overreaching due to hind engagement when in reality the horse is clipping because they lack freedom and full reach from the shoulder through the neck and poll. Imo in that vid the lines need to be looser and the horse needs to stretch and reach for the contact rather than brace and false frame against it.
I find side reins easier (less complicated) to use bc I can simply make them loose enough that just the weight/motion of the reins on the bit as the horse moves encourages them to stretch without causing bracing while they are too long to make the horse false frame or duck. I prefer a horse slightly above the bit moving forward than one slightly behing where the energy block occurs just behind the withers.