I think the way you handled shields is just brilliant. Many many other systems struggle with having shields reduce the chance of an attack making contact, or add to DR. Some do both. It never feels just right, and I see shields remain mostly unused.
Having it add to your resistance checks makes the shield much more useful since you can help offset disadvantage penalties (incoming arrows!) help with blocking (resistance check) and even save your bacon from Dragon's fire since it helps with your resistance check that might otherwise would bypase DR.
That is why I say, Brilliant!
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Agreed!
This is how I've handled Shields in D&D for years. They gave a bonus to AC and to Saves v. Breath Weapon/Deflection. BBF's independent use of this mechanic was one of its obvious points of clear and rational thinking. :)