Mercury Glass is distinct among the many types of Art glass.
Silvered or Mirrored glass has nothing to do with mercury and was never used in the formula that made the mercury glass tableware.
The differences in decorating techniques will help to establish the country of origin, sometimes the maker clue is found in the seal. If you are collecting, this is important.
The value depends on it’s rarity, type of design and condition. Not unlike any other arena you might collect in.