They are one of those tools, Ray, that doesn't get used a lot. 90% of the time, an Indicol holder plus Interapid indicator will do the job nicely. The weird set ups are where the Co-Ax pays for itself.
One part had an internal circular machined feature located a couple of inches below the top surface, and there was no way a dial test would get in there. The Co-Ax, with extension tip, took care of that in minutes.
Another plus for the Co-Ax is that it's really fast. Get the part eyeball centered, set the feeler to contact the feature you want to indicate, start the spindle, dial X & Y until the needle stops wiggling, and set both dials (or the DRO) to 0-0. Pretty nifty.
Be sure to order the extra tips after buying the Co-Ax.