They are a great boot, and the fit will vary between model lines. The proton series has a little more volume in the boot, a 100-102mm last depending on model, with a higer volume instep area. They also have a larger heel pocket. The kryptron series is all around a lower volume boot, its obv a different sheel disign, the 3 piece setup allows the boot to have a much smother and equal feeling flex.