Neck Reps

[Papi93]

You going to be working you neck flexors with that exercise. If you go with 20 reps, you will be building local muscular endurance. Lower the reps into the 8-12 range for hypertrophy work. If you really want to hypertrophy the neck, I would go with compound exercises like the deadlift and squat. These will hypertrophy the neck more than any isolation exercise.

[Papi93]

A neck machine would be a better option than the plate on the forehead method. Problem is, not many gyms have them. In my experiences, the single-joint exercise that got my neck the thickest was shrugs.