The Four Tools
Vocably is the only one of the four that treats iOS as a first-class surface — a real Safari extension plus a strong app — so a word looked up on the phone and a word looked up on the desktop end up in the same deck. Its extension user base is by far the smallest, which is the usual risk: a small product can stall or disappear. Reviewing happens in its own mobile app.
Readlang is the cheapest way to turn ordinary web reading into flashcards. Every lookup becomes a card by default and you prune afterwards, which is the opposite of Vocably’s deliberate save. It exports, so it does not have to own review forever. Video support is weak.
Migaku is the maximalist option: it works across YouTube, Netflix and Disney+, produces rich cards (sentence, audio, image, definition), and ships both its own SRS and Anki export. It is also the most expensive and the most Chrome-bound, with no Safari extension. It is the right answer only if immersion from video is the main study method.
Language Reactor dominates on installs because its core dual-subtitle video mode is free. It is a video tool first — website lookup is limited and mostly goes through text import — and its review side (Phrase Pump) is thin, so it is normally paired with Anki rather than used as the whole system.