Why not just stay with BOI for their 5 yr fixed? It's 3.99 - AIB is 3.86%. Not much of a difference and no legal fees and probably quicker and less hassle. AIB might not even accept you. Speed might be important in case the fixed rates rise soon.
On a 200k mortgage over 25 yrs the difference would only be €14 a month or €840 over the 5 years. The legal and valuation fees would probably be that much and you would need to find that up front.
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