Bus Eireann is painfully slow (2 hrs 15 mins - 2 hrs 30 mins) as they have to serve all the little bypassed towns and villages as well as diverting into Shannon Airport on the way. However, the Citylink private bus service is only 90 minutes.
One of the big problems they're going to have is breaking the mindset of bus users. Bus Eireann still transport far more passengers from Cork to Kerry, even though the train is faster and cheaper. People don't consider the option. And even among those that do, they seem frightened of the (sometimes needed) change at Mallow, believing they're going to get stranded by a missed connection.