Actually I tried those for the first time a few hours ago and I didn't like it. Seems like too much wear and tear on the scalp.
If you have a well fitting helmet lying around you could give it a shot. Judo guys do 360 bridges a lot and have necks like the Disappoint Dad. Never met one who said he lost all his hair from bridging but I know what you mean. It's not so much the pressue as the slide 'n shear.
I know you said you wanted to work the back but for the front just lie down and hold your head off the ground. Nod yes, shake no, ear to shoulder, whatever, for several minutes without putting your head down. Harder than you'd think.
