I have a suggestion as well. I tested this plugin in Alpha theme and there is a issue when you are not logged in. If you are not logged in, you can click on Save to add it to Favorite, the action shows a confirmation message telling that the item is saved but there is no save.
In olx.ro, if you do the same thing, a popup shows and tells you
Bravo. The ad is now saved in your favorite list
Important and useful: To permanently save your ad, you must be logged in to your OLX account.
From that point, there are 2 situations:
1. you do not login/register BUT the ad shows as Favorite, even if you are nor logged in.
I can close the tab (and site) and if i open a new tab, the listing still shows in favorite list - so i assume it is a cookie
2. you login in your account and the listing is saved permanent to your favorite list
So, as it is now, this plugin needs the same flow or, if not, the Save button should be hidden to all listings until you log in.