This is the first glass nail file/buffer I've tried and wow: It's amazing! And it's a pretty sweet deal considering that it includes a protective cork holder. It works on the nail edges and on the surface to remove ridges, buff, and polish the nail to a glass-like shine, in just a few minutes for all nails.The pictures I've attached are of the Mr. Green file next to another glass nail file (Mont Bleu). The Mont Bleu file is etched on both sides in a completely different way (more similar to traditional files); doesn't double as a nail-surface tool (unless you want a super-rough nail surface); is about half as thick; comes in a thin, non-protective plastic case, and comes from Czechoslovakia rather than directly from Amazon, with a steep shipping charge and requires signature upon delivery.With the Mr. Green file, in a few swipes I got a gleaming finish on each nail surface, and with a few more I sculpted the ends of the nails in a way that sealed them to help keep them from developing chips and cracks. My nails look fantastic and feel far healthier and harder. The file did produce dust that seemed like more than just nail material, so I take it that part of the dust may be glass. In researching glass files, I learned they eventually wear out but should last at least a year. Other sources say they last forever.The Mr. Green file is etched on one side only. The other side is rounded and smooth. However, this makes the file thicker and less prone to breaking than most others. I suppose a nano glass file with both sides etched might last longer than this one (if it doesn't break); it's a tradeoff. The etched side of the file seems quite coarse, but that doesn't seem to matter; it gives a much smoother and more durable finish than my beloved Zen-on superfine metal nail file (which I bought decades ago at a guitar store and can no longer find). I was curious about why this is the case, so I read up more on glass/crystal nail files and learned that they fuse the keratin and help keep nails from cracking or chipping.The Mr. Green file fits very snugly in the cork holder, which seems protective. I might suggest making the container narrower, though, to make it more easily portable.So, goodbye, four-step, few-use buffers: You always disappoint. You wear out after several uses, take much longer per nail, and leave nail edges prone to developing tiny chips and catching or splitting in a matter of hours.Note: This file is not well suited to cuticle care, so I hope Mr. Green comes out with a round glass cuticle tool.I'll try to remember to update this review after using the file for six months or so to report on longevity.