Some of these shops are great for up close and some are alright.

But it initially depends on how you use them.

It initially depends, my assets do not have baked textures like albedo, specular .etc , they are simply setup in blenders node editor where i have compiled multiple textures, and sometimes even using procedural methods (example: noise texture), as a result you can import the model into another 3d software, but the textures may not look as good as they are in blender (only applies for various models) (unless if you add your own textures in that external software)