Hey there, ex-GCSE student here
I used many different resources during my GCSE years and for Seneca I would say it's good for foundations and basic knowledge- perhaps to quiz yourself after class to identify your weaknesses. Other than that, that's all it is and I would not recommend at all to use it on its own.
As for premium, my friend had it and said there wasn't much of a difference so again, I would not recommend so perhaps you could find something else?
any questions do let me know!