Impractical on so many levels:
- You have to bend down to use it- not good for grandpas or other people with accessibility problems.
- Water and grit ingress will be a problem.
- In Winter it will be covered in snow
- The gravel they spread on the sidewalk will scratch the glass in no time.
- When it is wet it will be all dirty and nasty.
- Will have to withstand cars stepping on it and wheels rubbing against.