The only numbers I will ever spell are one and zero, and only when using them as a pronoun, or for emphasis, respectively.
Is there ever a reason to not to use symbols when dealing with numbers? Why would "fourteen whatevers" ever be preferable to "14 whatevers". It's just so much easier to read numbers as symbols, not spelled out.
(Caveat, not including multipliers, like "273 billion").
You're in an engineering community, is ten-one actually wrong?
Consider the sequence: One, eleven, twenty-one, thirty-one, fourty-one, fifty-one... One hundred and one.
As far as the convention of writing numbers out in words when they're less than 10, there's also conventions for less than 15, wikimedia uses the convention if it can be written in two words it's optional to write it out as words.