Good point, isolated outputs will sync to whatever they are driving so are totally safe. It is rare though, many manufacturers don't even bother with isolated inputs as required by the latest NMEA 0183 spec. So finding any with isolated outputs (that are not required by the spec) is to be applauded. Life would be so much simpler if everything was isolated as standard, too much to hope for in this cost cutting world though.
--= The NMEA Specialists =--