I have one eye that's more dominant than the other, so I prefer a single Baush and Lomb loupe. Around 3.5x, 4x, 5x...any stronger and I'm too close to the piece to be manageable.
I'd asked the dental hygienist about hers and she loved them. The brand was Orascoptic. Ended up going through the process and getting a pair. Unlike everyone else's experience, I have a generous depth of focus on mine; about and inch and a half. I also got them for a special application and had a need for a specific focal length, so I don't use them for hand engraving, but all of my requirements were not a problem for their manufacture.
A sales rep made an appointment to call on me and brought a sample kit of the styles they offer. He proceeded to get me fitted and took measurements and wrote down my specifications. It took a few weeks for them to be made, but they work great. There is the need to get used to keeping your head fairly still, but not really immobile.
I use them for operating a rose engine lathe. My eyes are about 22" away from the cutter when I'm in the normal operating position. It's too far to see the fine details, and the depth of focus is what makes these binocular loupes work for me. They had a version that has multiple magnifications, as well as several models with fixed magnifications. The range is around 2.5 x - 4 x. Because of the variety of work I do, I chose the multiple magnification version. For dentists and dental hygienists, illumination is a big concern, and they have a number of lighting options. For my application, I have plenty of lighting, so I didn't need that as part of the package.
The company primarily sells to the dental/medical market. The sales rep had never sold a pair in the jewelry, engraving field. At the time I bought mine, they had a no-interest financing option, and I took advantage of that. They are, indeed, pricey. For me, the justification was that I couldn't really operate the rose engine lathe without this kind of optical aid, so it was either bite the bullet or give up on using the machine. I find that I tend to use the highest magnification, so if I were to get another pair for engraving, I probably wouldn't get the multiple magnification version, and that would save a fair amount. I have and use a microscope, so I don't have an immediate motivation to get another pair, but absent a scope, or if being tethered to a scope isn't desirable, the ability to get them ground to the focal length I need is great, compared to hunching over the work while trying to get my glasses or Optivisor in focus.
Hey, hey, hey Sam! Now your encroaching in my territory! Actually guys, I used Orascopic surgical telescopes for decades and loved them. However, they are not powerful enough for most engraving purposes. They do have a reasonable depth of field and can help with a lot of hobby purposes, just not as helpful as a microscope.