I checked them carefully myself with various other tools. It was using python to do the math so I trust it to a single standard deviation at least.
They probably meant that they could read (and trace) the logic in Python for correctness.
I would recommend spending that "couple thousand" for quote(s). It's a second opinion from someone who hopefully has high volume in your local market. And your downside could be the entire system plus remediation, fines, etc.
To be clear, I'm not opposed to experimenting, but I wouldn't rely on this. Appreciate your comment for the discussion.