Hold up!
You may want this version instead:
NEW Multi-Material - Static Mesh Combiner (Still FREE)

✔ Supports HDRP 2019.3.2+
✔ Supports URP 2019.3.2+
✔ Supports Standard 2018.4.15+

Guaranteed Support!
Your satisfaction is my top priority! Please, by all means, do not hesitate to send me an email if you have any questions or comments.
lylekgames.com/contacts

Static Mesh Combiner
♦ Optimization is absolutely necessary in any game. So here is a free tool to help you optimize your static meshes - the easiest way possible!
♦ Just a single click! Tools > Combine > Static Meshes.
♦ You can also disable your combined mesh, with no harm done to the original meshes.
♦ The new mesh will also retain its pivot point and orientation in the world.
♦ You can now save your combined meshes as prefabs!
♦ Only works on objects with the same material, so this may be most helpful when using texture atlases.

How to Use
♦ Parent any number of meshes, with the same material, to an empty game object. Select the this parent object and choose Tools > Combine > Static Meshes.
♦ Your meshes will automatically be combined, and a few new components will be added to your once empty game object. These components included: a MeshFilter, a MeshRenderer, and CombineMeshes script.
♦ Through the combine script you will have the option to save the newly forged mesh as a prefab, either as Destructive (child meshes are destroyed) or Non-Destructive (prefab is created with hidden child meshes), or to Disable the combined mesh, with no harm done to the original meshes or materials.

Tips
♦ There is a vertices limit, in Unity, for any given mesh. The combination of meshes cannot exceed this limit.
♦ Combining ALL of the meshes in your scene may not be ideal. This will force the game engine to render large portions of the game that the player may not even be able to see at the current location. Try to balance this for best performance.

Please, by all means, do not hesitate to send me an email if you have any questions or comments!

Website
lylekgames.com
Support
lylekgames.com/contacts

Same Material - Static Mesh Combiner