I'd get the standard Opti-visor. It has real glass lenses, so they don't get scratched like the plastic lensed LX version will.
One option is to have an accessory loupe model. This is a small round jeweler's loupe mounted on the side of the lense. You can pivot it up out of the way or turn it down in front of the main lense for extra power.
Personally, unless you're working on really small parts, I never found the loupe accessory to be of much use. If it was that small I went with my standard watchmaker's loupe.
Another option that might be useful is the light model, because you never have enough light.
As for what focus to buy, just sit down and position some work where it's at a comfortable distance away, then measure the distance from your eyes to the work. Buy a visor with that focal length lens.
The Opti-visor is the best and is a standard in many industries.
I got mine in watchmaker's school in the 1960's. I used it every day in some watchmaking applications, gunsmithing, and hobby work.
It's still in use today, although the leather head band pad has been replaced many times, and the band has been repaired several times.
