Superwhisper runs speech models on your own Mac and lets you configure everything. Speaky Box runs in the cloud and configures itself. Two good answers to different questions.
Speaky Box's prompt structuring works out of the box. In Superwhisper you can build something similar by writing your own mode and prompt.
Superwhisper downloads speech models to your Mac and runs them there. Nothing leaves your machine, it works on a plane, and you can pick bigger models for accuracy or smaller ones for speed. Speaky Box sends audio to a large speech model in the cloud and gets text back in about a second, then deletes the audio. Local wins on privacy and offline use; cloud wins on accuracy per second and on not having to think about it.
Superwhisper is a toolkit. You create modes, each with its own prompt, and switch between them. If you enjoy that, you can build exactly what you want. Speaky Box ships with the modes built in: Dictate for tidy text, Smart for app-aware writing that already knows what a prompt, an email and a message look like. You can edit the prompt template and add your words, but you don't have to touch anything to get started.
Speaky Box's Smart key turns a ramble into a structured prompt automatically when Claude, ChatGPT or Cursor is in front. Superwhisper can do this if you write a mode for it and remember to switch to it. The result can be as good; the difference is whether you want to build it.
Both let you add vocabulary. Speaky Box's Words list is applied to both keys and to every app. Superwhisper's depends on the model you've chosen and how you've set the mode up.
Speaky Box: free for 2,000 words a week, £8.99 a month unlimited. Superwhisper: a trial, then a paid licence (see their site for current pricing). Superwhisper has no per-word limits because nothing runs on their servers.
you need offline, you want nothing to leave your Mac, or you like building your own modes and picking your own models.
you want the best accuracy with zero setup, and you want prompts, emails and messages written properly without configuring anything.