The difficulty according to Valais Alps East Selected Climbs by L Swindin and P Fleming (1999) is PD for each part of the traverse. There are 2 reasons for which I believe the entire traverse is more difficult.
1. climbing the entire ridge from the Mischabelhütte to the Bordierhütte is a long trip which is frequently underestimated in time
2. climbing in the direction of the Bordierhütte implies downclimbing the NE face of the northern summit of Balfrin, which can be very tricky when icy and definitely harder than PD