First card is an Ace -- 4/52.
Second card is a Ten of the same suit -- 4/51.
Probability of suited blackjack: 2*(4/52)*(4/51) = .012066
We are gaining an extra 1.5 units with probability .012066, so this rule would add 1.5*(.012066) = .018099 = 1.81% to our expectation.
This is for single deck.
Casino Royale has this rule when you get a new card -- it used to pay off on a $100 max bet, now it only pays this on a $25 max bet.
--Mayor