In general, when it comes to Anki flashcards, those cards are only useful if you have actually learned and understood the material first (usually done outside of Anki).
Once you learn and understand the material, then the flashcards on Anki reinforce what you've already learned and help you to study and memorize it.
Now, in terms of the Pronunciation Trainers specifically, the ReadMe file that came with the Pronunciation Trainer strongly suggests that you watch the relevant pronunciation videos, so that you learn the Pronunciation Rules first.
This is made available to you for free and the link is provided in the ReadMe file. It is important to watch these videos as it will give you the foundation to learn accurate pronunciation; how to hear, produce and spell the sounds of your target language.
Once you have a better understanding of the rules for pronunciation, you can start using the Pronunciation Trainer deck in Anki to apply what you've watched in the pronunciation videos.
According to the Fluent Forever method, this first step of becoming fluent in a foreign language will take approximately 1-3 weeks to complete. Keep in mind that this is only the first step to learn a foreign language and it is recommended to read more of the Fluent Forever method in the Fluent Forever book, to get a better overall understanding of the method.