I actually looked at them but balked at the $130 price tag, at least for now. Also, when looking at the fitment if the head rest, I saw a video about some helmets having a tightening device in the back that is exactly where the back of your head / neck is supposed to rest on it. My helmet does not have that device, but does appear to have stuff right where the head rest is supposed to support my head. After buying the trike, then spending another $300+ on new shoes (clip-in), lights, bracket and case for my phone, flag, tubes, pump, etc., I just could not justify the head rest and a new helmet at this time. If I keep riding regularly, and I have any neck soreness, I might rethink the headrest in a few months though.
Also, I am no expert, but I feel the neck rest is more important, the more reclined you ride. I ride more upright. Head rest or not, if I have to have my neck bent in such a way that my chin is close to my chest in order to see where I am going, my neck will be sore no matter what. Maybe that is my lack of flexibility thing I talked about earlier affecting my personal judgement, so take my rookie opinion with a big grain of salt.