Comfort mainly. The Manners is just as strong but not as comfortable to me. They feel like a 2x4 bolted to my rifle, functional but not as comfortable. When I received my Manners T-5, there were several areas of the stock that were not true to one another.... just didn't seem to be of the same quality.
Like I said, I have more Manners than McMillans however, I still prefer McMillan.
t