Tubing anchors rarely get much attention until one fails. A string that moves under load wears the casing, buckles the tubing and shortens pump life, and by the time it shows up on a dynamometer card the damage is already done.
Dan’s holds the full range because the right anchor depends on the well: rod pumping wells that rotate, wells where hydraulic setting is the only practical option, and wells where the problem is rod rotation rather than tubing movement.