Yeah, but that only does ONE diff.
(image stolen directly from the Inchworm site)
I can see why some people would pay for his kit, but IMO $75 for a bunch of wire and zipties, a switch, a light, and some crimps is crazy. Plus, it doesn't include the harness you need to connect to the actuator (unless you cut the connector off and hard-wire it). I probably have less than half of that in my relay box, and it does BOTH diffs.