Gustav Merz founded his namesake and operated in Zurich, Switzerland as a goldsmith and jeweler and is said to have his family roots from Germany though we do not know for sure.  It is possible that Gustav Manz had some relation/ or was the same person and opperated from Zurich for some time.  Please see information on Gustav Manz.  More information is needed and welcomed!  If you have more information please let us know!