No joke.

I am 63 and have been doing the neck weight exercises since high school (as well as a full routine of weight lifting). I do the neck exercise in all four directions although for cycling you only need to do it in one direction, strength balance is best for your body.
Although my neck exercises have been intended to prevent neck injuries while playing football and rugby, plus military duties, the exercises do work well for cycling.

I am not suggesting anyone should jump in with the 25 pound plate like shown in the picture, but using a 2.5 pound plate would work great for a starting point and still be great for cycling.

If you are going to use this exercise, I strongly suggest buying the head harness and not rig up something on your own. A home rig might slip the weights and cause a severe neck injury from the sudden weightlessness.