You can hold plates on front, back, and sides easily. For rotation tie a wide band to a pole and wrap the other end around your head clockwise or counter. Friction will keep it from unspooling just fine.
Ok extensions are kinda a PITA but harnesses are like $20 on amazon. Got one in the cart atm.
The operative word was "conveniently". With the Nautilus machine, you just go in, set the weight with the pin, adjust the seat and you're ready to go. Front, back, both sides. Then he had another machine that worked the twisting motion as well. Pure genius that has never been duplicated.
Resting weights on my head is not easy and not comfortable. You're telling me you balance a dumbbell or plate on your forehead to work the front neck muscles?
And the harness is also a pain, especially in a crowded gym. It's not so bad for working the back of the neck but the weight swinging is a pain and can be dangerous. Forget about working the front and side of the neck.