Hello. I would like to add something to this... I also encountered the Mustains of Finland during my research. It does appear thought that the family of Mustain (as is is spelled are related to the shipping families of Holland and France) The name Taine/Mustain is certainly very Old Goidelic and variations of the name are liked to the migration patterns of the Gaels/Cymri.
The oldest encountered form of the name appears to have been Taine/M'Taine which predates the Finnish use of the name.