When I came across the app (I think it was on reddit), users were recommending that you set up another account in case Spotify catches on and bans your account (so you don't lose your favs/playlists/etc)
And that's what those people (not me) did, they set their original account playlists to public so they can be accessed by the second account.
However for as long as they (not me) have been using that app nothing has happened to their account.

Also just checked, they (not me) have been using that app since august 2021 with zero problems.