I love the decision its a very smart move. He can't stay on the field, 10 injuries in his very short, young career that is way too many. Prove it. This guy needs to step on the field and produce 16 + games and EARN his next contract. The days of just giving Bills players contracts is over, they have to earn them.
As for as the money, who cares? Right now we are due to have over 30 mill in cap room BEFORE it goes up. 5th year 13 mill, Franchise Tag 17 mill, who cares? The smart move was to say no and make him earn it and that is what McDermott did.
IF he performs, try to extend him. If he says screw you, Tag him. This is simple folks.