Hello,
If you have a copy of the original loan agreement, read it first and see what terms and conditions are contained within (particularly with reference to a tracker rate and what the lending margin should be, over ECB).
Assuming the rate is the same as the one your now quoting and it's not a lower lending rate (i.e. margin over ECB) then I'd personally take it without thinking twice.
If you do not have a copy of the loan agreement, ask them for a copy before you can respond to their letter, so you can cross reference both.
Experience over recent years has shown, those with Tracker Rates are better off and I expect, that will continue to be the case (because variable rates are subject to the Banks in house decisions on rates and with the Banks needing to earn more profits, it's very clear whats going to happen here in the years to come).
Regards
Mr. Earl.