this is good to see. i also trained a stt under 500kb for sub dollar chips. it had about 20 words that it could understand(like start, stop, left, right, go, up etc) and then the spell mode where you could say the word spell and then say the individual english alphabets and close with spell. it was super fun to work on. these tend to be extremely unstable though, like confusion between p and t (at least for my accent). will have to try this one now.
Could you get people to use the NATO phonetic alphabet for the spelling part? I suppose a challenge is that many people don't know the whole thing, even if they're aware it exists.
NATO phonetic is to be understandable over a noisy radio channel, if you want just distinct sounds then Talon Voice users settled on shorter ones easier to use all the time:
Interesting, that some words don't start with the letter they represent.
“Plex” ?
I remember someone training smart kettle to use its speaker as microphone
IIRC the Alexa enabled voice remotes also used a similarly small model though perhaps not this small