It will, hopefully, bring in a lot more connecting traffic for Aer Lingus. If you have to connect somewhere to get from europe to your final/intermediate destination in the States, you may as well use the 2/3 hours allowed for your connection constructively by clearing immigration and customs, freeing you at the far end to just walk out of the terminal instead of "joining the line" for up to 2 hours. For some they will see this as a time saver for others it is only the cost of ticket that is important, so it is important that EI get the transit process and the price right. I am NOT suggesting that people will abandon LHR/CDG/AMS in their droves to transit through DUB, but it is a useful facility to have, that will be seen as an advantage to some travelers.