There's an actual program, and a saas version. The saas version isn't worth paying for (imo) over using AnkiWeb unless you wanted preformatted decks, and the most up to date version of the algorithm.

I've experimented with using the website (mostly because I'm a fan of the software). It's mostly okay. I've been using Supermemo (the actual app) for a few years now on a daily basis. The app itself has a trial if you can find a download link somewhere, and I believe the site might be free if you import your own decks.

As far as lock in, I believe you are also locked in unfortunately. This would be another reason to go with Anki or another solution if you just want flashcards.