Point 1: You can use advanced navigation views to create custom navigation trees and then associate the custom navigation for a user and then restrict the user to this navigation tree.. the catch is links within the navigation tree may allow them to exit the navigation tree and access areas you do not want them to go so you need to watch out for this.
Point 2: Agreed, as well there is no access controls around the Key Displays and once you add a key display it is viewable to all users. The only current work arounds are: A) Create a custom navigation view with the displays you want and then not utilize Key Displays at all. B) Utilize Key Displays and lock users homepage down to a particular screen but completion remove their ability to access the navigation panel.
Please be sure to communicate the request to have folders and access controls around Key Displays to your account manager and ensure a "Product Commitment" is entered.
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Christopher R Souser - Solution Architect – MSci. PA, CISSP, ITIL.