It does indeed make Twitch easier to use, removes the clutter from the screen, gives basic QoL improvements that should already be there, plus lets you see deleted messages. Personally, I would add an uptime clock below the stream (like how FFZ does).

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Some of the customization options like showing the deleted messages or splitting chat just stopped working on the latest version of Firefox

Twitch without bttv is like gaming without a monitor. A tough challenge.