Photo Gear Designs Tracker Kit, Includes ESM-1 External Sight Mount, CR2032 Battery, Hi Viz Storage Pouch

This is a niche product for sure. If you need to track flying birds, airshows or other fast moving subjects, than this is the tool for you. What you are paying for is the machined mount that attaches the dot sight to your hot shoe. It does come with the dot sight, but it isn't an expensive one (doesn't need to be for intended use). The inexpensive mounts can move or rotate each time they are attached to the hot shoe. In all fairness, the hot shoe was not designed for precision alignment. This mount solves that by attaching in the same position each time. Yes, there are cheaper mounts, but they all require recalibrating when you re-attach. Calibration isn't hard to do, but it takes a tripod and hex key each time. That can be inconvenient in the field. These could probably be made cheaper if there was a bigger demand. Considering what photo gear can cost, I think this is a reasonable price if it is a tool you will use regularly.

First off there is no use for this, why place this bulky piece of equipment on top of the camera. Second $150 is wayyy overpriced for something that cost most likely $50 to make if you did this yourself. Save yourself the money and either skip this or just make your own.