Apparently it's a nag-based paid software with an otherwise restricted feature set. This is not clearly explained on the page.
In fact, it looks like the site goes out of its way to try and pass for free software - the Demo is NOT of what you are actually downloading, no pricing info, no mention of Basic vs Full versions anywhere, including the Docs, except for an dull looking blurb at the very bottom on the home page -
License
Files is free to use with basic features. To remove the
license-popup and unlock additional features, you may
purchase a license [$39] from within the app.
The page also pulls a lot of scripts off the Internet on every load, so that too is not explained anywhere clearly and it's absolutely not good for hosting private photo archives.Despite its good looks it kinda leaves bad aftertaste because of all these shady shenanigans.