Thier is no need to replace, you can reuse for many years to come. All you need to do is run it under some warm water and with any nail brush or old toothbrush and some antibacterial soap clean pat dry it and let air dry for 24 hours and it should be normal again.
I've read that's they're great for smoothing out bumps, discolorations, and for shaping the free edge of the nail. However, It’s not very effective when trying to file down a lot of nail length. Also, because it's glass, it can break easily so you have to be gentle with it.
There are different grits to glass nail files, but even the grittiest that I've encountered, tend to smooth over after a while. So glass nails files, generally, may not be very helpful for particularly strong nails.
Glass nail files are typically used for delicate baby nails. They are also used in salons for people who get Gel or Acrylic nails removed, as their nails have been weakened with the enamels filed down.