FIFU is compatible with most popular plugins. If you intend to use the Premium version with a specific plugin, try to test with the free version first.
You can continue using the Premium version normally*. However, to continue receiving updates and support, you will need to make a new payment.
* except the features “Auto set featured image using post title and search engine” and “Auto set featured image using ISBN and books API”. They run on a cloud service, so there are ongoing costs.
For other questions, support@featuredimagefromurl.com