I never had a issue with units conversion and qnh/qfe utilization in spite of equipment and rule difference.
Try operating into a Chinese airport a few hundred feet AMSL which uses QFE when you have an altimeter reading in feet and your company uses QNH. Basically you set QNH on the altimeter and have a conversion chart which gives you the number of feet to set on the FCU in response to the controller's instruction given in metres referenced to QFE. This chart is unique to the airport and obviously differs from the standard feet/metre conversion chart.