[rmrector]

Seems to work, but with a strange behaviour:
The fanart is set correctly and shows up in the artwork select dialog of a DB item, but ListItem.Art(fanart) returns an empty string.

Edit:
Tried it on a different setup with the latest nightly of today and the problem is gone. But if I set to fanarts to 1 it will add 20?

That limit is for artwork grabbed from web services, it will import all artwork in the filesystem. If you have multiple fanart in the filesystem, presumably you want Kodi/skins/addons/etc to use them, and integrating them into the library provides a lot of benefits for using them. This forum post (under Why?) has an explanation of the benefits.

Even if you aren't using a skin that uses this method of gathering fanart, I don't expect any performance issues with them being in the library, even on a low powered device. I don't actually know how it performs on such a device, so I would appreciate any reports.

Though there aren't actually any skins that use this method. I haven't yet done much to sell this method to skinners as Artwork Downloader may be updated with a method for multiple artwork at any time, and could easily conflict with the way I've done it here. Maybe I'll start; after so many months that may no longer be a very good excuse.