Davbo,
Agree w/ Nikki, that is for people who still have the motion, just need more of the prompt.
Could suggest better alternatives if you could share whether you need support front to back, side to side or both. And whether you had any kind of collar before you tried the Headmaster, and whether you need support all the time or at certain times, e.g. will you be using in the wheelchair, sling, or...?
As far as the "high end" collars, the only one that Larry had any success with was the TracCollar, also available on the site you linked to. But that was only a last resort; most of the time he used the Embrace Sleep Collar (not when sleeping!) or the Ita-Med medium density cervical collar.