My point is that 'it costs money' is sadly not a way to gauge good calculators on ios, and a lot of the 'costs money' ones don't even have a free option to test/check-the-precision.

Note that I never said cost was a way to gauge good calculators. I was merely answering the question of why one might pay for a calculator app instead of using one of the many free ones. Again, this is why I very deliberately said "might" in all of my statements. By saying "might", I'm also implying "might not"...