To have 3 operators using up parking space and runway time to operate on the same route does not seem to be a very clever use of SOU's limited space.
Can't see that it will be 3 operators for very long though?
I guess the Q400 carries about as many pax per trip as the 328 and 135/145 put together, so this seems a bold move by Flybe - pricing alone may not win the day with the business pax.