You seem to think that double entry bookkeeping doesn't require extra work (significant increase in costs),
No, it doesn't. Entering the numbers into a cell in Excel spreadsheet or to the field of a bookkeeping software require the exact same amount of work.
Also, this is plutonium. It sits in storage and gets moved around only occasionally. And when it does, accounting is the least of the expenses - or do you simply send it in mail?
that it wouldn't reduce usability (far more difficult to produce reports on wider issues),
This is a thoroughly bizarre statement. How is a software specifically designed to handle this type of task less usable than a generic spreadsheet? What "wider issues" does it keep you from reporting?
or that it would make system immune to human errors.
No system is immune to mistakes, but some are inherently more resistant than others.
You are incorrect on all accounts.
And you are making such bizarre statements I doubt you know what double-entry bookkeeping means.