For completeness, by law every lender must provide flexibility to overpay, but may charge a break fee for early payment during a fixed rate period.
Those that allow overpayment without breakfee:
BOI: allow regular overpayment of the higher of 10% of normal repayment amount, or 65 euro. Not lump sums.
Ulster Bank: 10% of the fixed balance each year, by regular payment or lump sum.
KBC: cumulative 10% of the fixed balance during the fixed term.
Finance Ireland: 20% of the balance in 12 month period, by lump sum only.
Avant: 1% of the fixed balance per year.
And those that don't allow overpayment without calculating break fee:
AIB
EBS
PTSB - however, with PTSB if you make an overpayment, but don't tell them to either reduce term or amount, my understanding is that no break fee is triggered. This is a 'process' so I wouldn't place reliance on it.
Interestingly, as the topic is about longer or shorter terms, most of the lenders will allow you to contractually shorten the term without triggering a break fee calculation. So you end up overpaying every month, but you're signing up to that permanently.