It's got a Windows key so can't be anything terribly exciting. Any dates on it?

There's a model number and FCC ID on that bottom pic. I can't make them out at this low res, but either should give you info on what this is. It looks late 1990s, and nothing other than that "ARM" suggests it might actually have an ARM architecture rather than regular x86. Decent chance of a K62+ or a Dixon P2 though.

I've seen that case design before with various different brands on it - generic store brand. Pentium 1 from memory. Terrible DSTN screen.

Yes, looks like one of the generic laptops made in Taiwan for small brands doing re-badging in the 90's-early 00's. I have one such laptop with a very similar keyboard, made in 2002 with a desktop P4 Celeron inside (and absolutely inadequate cooling). Yours looks like made in the 90's and lower spec.

Try googling the Model number: green753+ . I’m seeing similar laptops branded maxtech but it’s very tough to get any info. One post on a forum from 1999 suggests the specs might be: Pentium 133.