Here is a good approach. Create roles for devices like "Android", "SmartDevice", etc.
In your Role Evaluation Policy, use those rules to Set Roles (Tags) for Devices, and make sure you have "Evaluate All". So A device could end up with the tags:
[User Authenticated] (built in), Android, SmartDevice.
You then use the Enforcement Policies (First Applicable) to check on the Roles, like if role Equals User Authenticated and Role Equals SmartDevice and Role Equals Android, set it to an enforcement profile that blocks access.
Long story short, Role Mappings are used to set Roles or Tags to Devices. Enforcement Policies are used to make decisions based on all the Roles (tags) that an incoming authentication has.