Miter saw laser guide retrofit

Here’s a nice add-on ($25) to a saw if you cut a lot of wood with a Miter saw and want/need a laser guide – “Projects a clear line just to left of blade cut. Replaces the outside washer on a miter saw. Self callibrating-sits flush against saw blade. Auto on/off-activates when spun over 400 RPM. Battery life: 1-1/2 hour or 5,000 cuts. Diode life: 3,000 hours or 2 million cuts. Includes batteries, case, installation bolts & key. Does not fit Bosch, Ridgid or Pro Tech miter saw.” – Link.