Brendan,
You are over complicating the maths.
If you borrow €100,000 over 30 years your average outstanding balance is approx €66,000.
The difference between 3% and say 1.5% of €65,000 is €975 p.a.
The difference between 3% and 6% of €65,000 is €1,950, and it might run at much more than 6%.
I accept that other better 30 year fixed rate offers may come along soon. My point was not that this particular offer is the best, but that 30 year fixed rates at these very low rates (by historical standards if not by some European standards) are a brilliant product.
As for people regretting fixed rates, well I have posted on here in the past that Fixed Rates are a bad idea, unless you really need the certainty because the bank charges extra for giving you that certainty. That in effect getting a FR is betting the you know more than the bank about the course of future rates.
But this is different (spot the opportunity for a cheap shot, I know you wouldn't stoop Brendan) in 2 ways: 30 years rates have never been available in ireland in the past, and rates of 3% have more risk on the upside than on the downside.