Please set your viewport and camera clipping to at least 200km ( 200 000 m)

No.

This tool was created to obtain renderings with a lot of details. While it has been mentioned above that this tool has been optimized to save your PC's resources, it requires a certain capacity to operate properly. Thus its use and the resulting rendering process require a certain amount of PC power. The tool was created with a medium power PC core i7 3770, an AMD Rx480 graphics card, Ram 16gigas. It is therefore recommended for the user to have a machine with equivalent or more powerful performance.

This is not related to the product but a general Blender issue. If you use AMD GPU the latest drivers may have issues with Blender 2.8+ and Natural Sky may not work properly. We've solved the issue by rolling back our driver to old versions.

A detailed guide is delivered with this product as PDF  file in the zip file.

You can download it from here too.

Volumetric is slow. 

Any project involving volumetric objects with Blender will be  slow no matter what the add-on or tool is. Natural sky has been optimized for better performance but slow volume rendering remains a general Blender limitation. Set render and viewport samples to less than 10 during scene creation, you can set the samples higher during rendering. Using denoiser is recommended also. Also when volumetric is involved CPU is faster for viewport rendering and GPU is faster for final rendering. 

Additional render setting Light path max bounces Total 12 , Diffuse 4, Glossy 4, Transparency 8, Transmission 12, Volume 8

Most of the issues are from people who are not familiar with Blender. Please do not buy this product if you're a very Blender beginner to avoid frustrations. It is recommended to have basic knowledge of blender software such as appending, handling of outliner and collections, changing camera settings such as clipping etc. This is the guide that needs to be followed in order to use the add-on, please be sure you can follow it.  It is also recommended to have previous experience with Blender's volumetric rendering in order to understand the constraints that go with it.