Compare to other addons
In Vimium , you can bind key-strokes to vimium commands. In Tridactyl, you can bind key-strokes to tridactyl commands and arbitrary JS code. Therefore, if you can write js, tridactyl can be much more powerful to you. (and steeper in learning curve)
With js, one can easily define pure keyboard mode on many websites. Enumerate every action on twitter/mastodon/github, perform them in js command and bind them.
You can call web-extension api in js context, so you can do nearly anything addons can do in tridactyl.
If other addons accept message from other addons,
you can send message (browser.sendMessage()) to them,
like Tree Style Tab or Webscrapbook Integration.
You may need to write the code to send message.
You can bind keys even in textarea or textbox (<input type="text">),
like bind --mode=insert <A-f> text.forward_word,
even bind --mode=insert <C-Enter> js document.querySelector('form').submit().
If you install the native-messenger, you can run command in system-shell, like open editor to edit the content in textarea.
You can define minor mode like video mode in How to define custom mode,
so you can use h l to seek in video.
Tridactyl is far from perfect. There are many bug/issue on github, and you are very likely to face some if you use tridactyl intensively.
The command expansion and js command is somehow awkward and not very instinct.
It can work fine but you have to know how to use it.
Tridactyl only work on firefox now. There is a old issue about porting to chrome: Consider porting to Chrome · Issue #1619 · tridactyl/tridactyl.
The js features can hardly work in Manifest v3, which forbid the eval.
If firefox deprecate the Manifest v2, the Tridactyl will nearly dead.