The banks use different methods for calculation of break fees. With base interest rates not moving for the past few years, break fees are miniscule in most cases except for AIB who take a different view on the calculation.
On the cashback deals. Some solicitors were doing deals for a multiple switch as the extra work involved was not extensive. However the banks have now caught onto the loophole and are now insisting on the mortgage being with the previous lender for a minimum of 12-24 months.
But do be ware of cashback deals. Banks are not charities and cashback deals usually cost the more in the long run especially if the bank has horrendous standard variable rates like ptsb or do not permit current customer avail of all fixed rate options (again ptsb are the worst in this regard).
But certainly if you have a fixed rate, check and see if one of the current fixed rate deals is better for you. The break fee in most cases is miniscule or zero.