I had two neck surgeries. The first surgeon used the collar, I had to wear it non stop for 92 days in the middle of a HOT Florida summer, yeah it was fuuuun. I was ACDF X2 with NO intrumentation.

Second was also ACDF X2 and this time I didn't have to wear that dreaded thing. I did have instrumentation this time and that is why I didn't have a collar.

Maybe that is the difference?