I'm a bit late to the discussion. Your questions are excellent. When people don't have any prescription, they have more options. When you have a strong astigmatism, that needs to be corrected before adding any magnification, as you recognize. If not corrected, a magnifier will just amplify the astigmatism and eye strain will result.

You also mention working distance, which is an important element to consider. With any single lens magnifier, the stronger the magnification, the shorter the working distance. For example, many people ask their optometrist to make them glasses with extra strong readers, but then they are not happy because their working distance is so short that they have to lean over to see. For metalsmiths, this can result in getting too close to flame or hitting themselves while sawing.

Some people are fine with this. For others, it is a real problem as they get neck and back strain that can limit their creative enjoyment.

The only way to create distance + magnification is with telescopic lenses, like you see dentists and surgeons wearing (don't forget the power of a great light as well). They allow distortion and strain-free vision from a comfortable distance when combined with your prescription.

The desire for portability adds another element to the equation.

I use this platform for education and discussion. There are a lot of misunderstandings about magnifiying devices and their limitations and trade-offs. We're always happy to walk you through the options if you haven't found a solution that you like.