Yes. Your daily stack, all deep dives and every review stay free with no time limit. Premium only extends, it never locks away the core.
Unlimited browsing in the Explore section, every fact available offline, and full stats on what you have already kept. By the way, Factucate is ad-free for everyone, including the free version.
If you plan to stick around: yes. €39.99 once and you never see a subscription again. If you first want to dip a toe in, the yearly plan at €1.25 a month is the best deal.
The subscription runs through your App Store account. You cancel there with two taps, effective at the end of the term. No calls, no notice periods, no hidden catches.