I'm using range slider and i try to attach scope value to the attr rzSliderPresentOnly.
My example :
Directive :
rzslider(rz-slider-model="formData", rz-slider-floor="0", rz-slider-present-only="readonly", rz-slider-ceil="100", rz-slider-always-show-bar="'true'")
Controller :
$scope.readonly = true;

I changed
this.presentOnly = (attr.rzSliderPresentOnly === true);
by
this.presentOnly = (scope.rzSliderPresentOnly === true);

and in scope declaration :
rzSliderPresentOnly: '@',
by
rzSliderPresentOnly: '=',

Example : http://jsfiddle.net/qv6cs01m/