That's a very good point.For example a 4 year fixed term at 3.1% with 2% cash back up front works out at almost exactly the same cost as 2.6% fixed with 1500 cash back (assuming a 300k loan).
When you allow for the additional 1% cash-back at the end of year 5, you could argue that BOI still has the more attractive fixed rate product for mortgages of €300k+, with an LTV up to 80%.