"Workman" is pretty cheap (mostly CB) stuff. I wouldn't pay anything for any of it.
I took one of their mag mount bases apart a year or two ago to find they were literally using the magnet itself as the electrical contact from coax outer conductor to the outside world, then a think piece of plastic between the magnet itself and the bottom of the mount where it contacts the vehicle. Then, I checked the electrical continuity of the magnet: Zero. There wasn't any, at all.
I have no clue how they thought that would ever work.
I use Larsen NMO mag mounts, which use a piece of thin aluminum as the contact between the coax and the vehicle, so there's a large capacitively coupled mating surface, and full electrical continuity between the coax outer conductor and that aluminum. They work fine, and cost about the same.