They are nice, but not needed. Properly fitted, the axle nut will install to the same location each time.
With the mains (mine is a 6A) on the ground, remove the axle nut and install the rod for the jack. When you are ready to install the wheel, slide it on the rod, slide the rod in the axle, jack it up and remove the block that you had under the axle. Push the wheel into place and let the jack down. Remove the jack and rod and replace the nut and cotter pin.