I have disagreed with much of Polax's comments, but when it comes to the IAA, I too lack confidence in them. They're very efficient with paperwork, when they chose to be (5 months to convert a licence isn't efficient, though), but regulation of the industry needs to be more than rubber stamping paper.
However, if they are such stringent regulators of safety, one has to wonder why so many other EU airlines have swapped from their domestic register to the IAA - Norwegian and several Italian companies spring to mind, and I think I saw some Baltic operators with Irish registrations too. The airlines won't have done that to face increased oversight and regulation...
And while the IAA may be self-funding, it is part regulated by the DOT, which is an Irish government authority. Whether is be by reducing the IAA burden on the DOT or paying funds directly tot he Irish government, the Irish government is benefiting financially from other nations' airlines transferring registries, and it all smacks of a flag of convenience. Shipping companies did not switch to Panamanian flags for safety benefits.