I was making a top down mobile game that would be in permanent portrait mode with all other orientations unchecked in build settings.
It bothered me that the Unity UI would be sideways when i held the phone in landscape orientation instead of adjusting the position, rotation and size of the UI elements to look good in landscape mode.
After a lot of thinking on how to solve this problem in the most elegantly simple way, I developed Mobile UI Rotation.
No more sideways UI or tinkering with object properties in code!
Visually modify gameobject properties when mobile device orientation changes, making sure your objects look perfect at any orientation.
Since the plugin uses unity’s animation system, you can technically modify any animatable properties.
You can see it in action.
https://www.youtube.com/watch?v=f2ZfsU6jkm4
It’s running with static portrait orientation, but the sensor orientation change is detected and UI is updated.
Check it out on the Asset Store
Let me know if this asset saves you time and provides value 
Thanks.