Your class will be very lightweight, so I don’t think the use of pointers with it would be of much benefit anyway. Just use pass-by-value or pass-by-reference, e.g. use it the same way that std::string or vtkVariant are typically used in VTK interfaces.
By the way, your interface uses parameters of type “const std::string” but that makes no sense and must be a mistake… did you mean to use “const std::string&”?