This material only works properly in Cycles (due to use of Bevel nodes in the shader editor & ambient-occlusion behavior). This is why all parts in the asset file by default have the simplified M_BasicMetal instead; as it works with both Eevee and Cycles but shouldn't look too different. Some adjustment to materials may be needed to get the desired look depending on the scene & lighting.

Switch the scene in the Blender file in the top-right corner, where it should say "Scene-Monobot" or "Scene-Arm".

The models are modeled and optimized for the Bevel and Weighted Normal modifiers in mind. If you don't want the bevel, you should be able to fix any shading issues by adding a Weighted Normal modifier with "Keep Sharp" and "Face Influence" both checked. Adjust the parameters until shading issues are no longer visible, and apply the modifier.

Adjust the Bevel modifier's "Amount" parameter. If you made an object smaller, make the bevel "Amount" smaller. If you made an object bigger, there shouldn't be any issues, but the bevels will appear smaller.