Instructions:
1)Install the addon as any other.

2)Find the Stack / Unstack UVs button in the UV side panel.

3)Select the objects you want to arrange the UVs of and click on UnStack UVs. It also doesnt matter if you are in object or edit mode. ONLY SELECT THE OBJECTS YOU WANT TO STACK BEFORE RUNNING THE TOOL. I prefer to enter edit mode, then run the tool so I have a preview in the UV editor of the layout after completion. Lots of heavy geo may take a few minutes to complete. 

Notes:

The addon works based on bounding boxes so make sure you have the same texel density across all your objects to expect correct results.

The ideal way to use this addon is to UV your objects and do your own layout for whatever mesh you are working with. Then instance the objects around, and when you are ready for the texturing process, break the instances, set your desired texel density and then run the addon to layout all of the UVs instantly. The script functions by looking at bounding boxes, so as long as your objects have the same/similar bounding box it will work flawlessly. Even if you delete parts of your geometry to create variation.

The UVs DO NOT NEED TO BE OVERLAPPING for the script to work. It will arrange them regarless.