Eagle Filer use without copying all FILES possible

That’s correct, however the folders need to be inside EagleFiler’s Files folder. You can choose whether to move or copy them.

If you’re using macOS 10.13 or later, even if you opt to “copy” it won’t use double the space. EagleFiler will use APFS file cloning to make sure that the blocks on disk are shared between the two copies of the files.