This can cause maintainability nightmares down the road. Over time, in a large software project, you will inevitably want to replace something that was previously a primitive with a method. In Ember you can do this painlessly; in AngularJS you’ll have to update every template where that model is used.
That’s your own fault if you aren’t using a getter/setter pattern in AngularJS. As my example shows, you don’t have to worry much since when you’re updating the model presumably it’s attached to a $scope in a controller. Thus, the controller’s $scope can watch the model for updates.