Anki is the gold standard for retention — the FSRS scheduling it popularized is the same engine behind Capecho's review. Its one tax is building every card by hand, and that's the exact friction Capecho removes: one keystroke runs on-device OCR to grab the word and its sentence off whatever you're reading — an article, a PDF, a video, your IDE — or copy-paste, no card-building. I leaned on Anki over the closed alternatives because FSRS is open and your words always export straight back to it.
I use it for a long time now. And you know what? I speak 8 languages by now. Not counting the programming languages, only the natural ones. And I use ANKI for everything, not only that!
Pros:Spaced repetition is the best scientifically confirmed way to remember stuff you need to remember. And here you choose what to remember!
Cons:No cons. May be the interface could be a bit more flahy but I personally do not care.