Platform coverage is the quiet dealbreaker in this category: a tool that only works on Netflix is useless the night your show is on Viki. Here's LangPanda's verified coverage and how it compares.
Confirmed supported sites
(from LangPanda's published list): Netflix, YouTube, Disney+, Amazon Prime Video, Hulu, HBO Max, Bilibili, Rakuten Viki, and Plex — with the full list running past 20 video sites. Support means the full toolkit works there: clickable subtitles, dictionary popups, saving words with audio and screenshot capture.
Why Viki and Bilibili matter.
Viki is where much of the K-drama and C-drama catalog actually lives — and since Viki discontinued its built-in Learn Mode, an extension is the only way to get dual-subtitle learning there; LangPanda is the mainstream option that supports it (our guide: Dual Subtitles on Viki). Bilibili is the natural home of Mandarin content. Language Reactor covers neither — its video support is Netflix and YouTube. Trancy covers more than Language Reactor (adding HBO, Disney+, TED, Coursera, Udemy) but doesn't list Viki or Bilibili either.
Browsers.
Chrome, Brave, and Edge. No Firefox and no Safari — if you're a Firefox user, Trancy is the maintained alternative in this space.
Mobile.
The browser extension is desktop; LangPanda's iOS and Android apps handle review on the go (your saved cards sync), not in-player subtitles on mobile streaming apps — true of every tool in this category, since mobile streaming apps don't allow extensions.