Credit monitoring services do not affect your score and are helpful in monitoring changes. I'm not sure about Citibank's, but I've used Amex's and TrueCredit.
I use both Amex's CreditSecure (which is through Experian) and TrueCredit. I've also used Equifax's CreditWatch in the past.
credit monitoring make sure the credit monitoring services monitor all three credit reports. Each of mine were different.
