Odd/rare blackjack rule value?

[kewlJ]

My brother found and has been playing a game (electronic), where the player is allowed to hit again after doubling down. The example would be dealer shows a 7, player doubles down on 10 and receives a 3, and is then allowed to hit again.

It is beyond my ability to figure out exactly what this adds to the players advantage, and I see no way to run a simulation based on this rule, but it seems like it might be worthwhile. Anybody, mickey, maxpen, have any ideas? Or perhaps one of the math guys from the other forum that reads could PM me.

Thank you.