Blackjack promotion

I stumbled across a promotion for blackjack. This promotion / added rule is for curtain days and is part of the main blackjack bet not a side bet. The promotion is an ace jack of spades pays 20 to 1. I noticed on the Wizard of Odds page that he evaluated a suited blackjack rule paying 2-1 as adding .57% to the players edge. That being said the rule he evaluated was for any suited blackjack and the promotion I found was for ace jack of spades only. That being said, even though the promotion I found has a lot higher payout, it would occur far less often. Can anyone tell me what this promotion would add to the players edge?

20:1 payout for player natural Ace of Spades / Jack of Spades?

Mental calculations, which may be misapplied. I post them in the hope someone corrects them if I'm off.
If you are playing at a full table, with other side bets, you could expect to hit one every four hours or so. and get paid an extra 18.5 units.
That is a little more than four units an hour, where you would normally be minus one unit an hour. I don't know the math, but in English, I think that's a huge edge.

Infinite deck. You will get spade suited blackjack one of every 1352 hands. If you get an extra 18.5 units each hand that is worth around 1.37% to the player.

In single deck you get the bonus once every 1326 hands. So worth a tad less than 1.4% to the player.

If the game has otherwise decent rules it is a player advantage game.