At times it has being cheaper to fly EI to FRA than FR to HHN. Would think yield per passenger is very high and FR may keep it at 4 weekly to maintain this. Only difference its 4 weekly year round where as KIR is 3 in winter. I have used it a few times and Loads ranged from full to 60/70%. The time of the flights are good as DUB-FRA with LH/EI are more less at the same times.
How are FR doing with daily BUD service? EI seem to be doing very well.