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I had a rather stupid large pair when I was in middle school. Never bothered wearing them to school though, for almost obvious reasons.
But now they've managed to more or less streamline them. How useful are they though? Is it worth picking up as a last ditch emergency set of glasses?
I've never tried them. In fact, I didn't even know there were adjustable glasses that work with sliding lenses: the only type I knew of is flexlible liquid-filled lenses. I've been looking for an explanation of how the sliding lenses principle works for the past 20 minutes but I can't find anything. Annoying!
I don't think they will do you much good if you have a lot of cylinder in your correction. But if you have none, they should work. Also, they look like the field of vision is very narrow. And of course, the elephant in the room: the dork factor is off the scale ๐
Maybe as emergency glasses
EDIT: here's a less dorky alternative - appears to work using the same sliding lens system: