If a cheaper offer comes along, and you are stuck with ptsb for 5 years, then you will regret going with them.
Ulster Bank offers its existing customers the rates available to new customers. That is quite a valuable commitment. In other words, if UB reduces their rates for new customers, you will be able to avail of them. If ptsb doesn't, sure you can switch to another lender. But will you still have the €10,000 and will you bother?
Go with the best long term value which is Ulster Bank. Actually, AIB might be a better bet, but you seem to have decided against them.
Brendan