Here are your approximate advantages in a BJ game knowing your first card has a 1 in N chance of being an ace...
N=
13: -0.42%
12: -0.06%
11: 0.36%
10: 0.87%
9: 1.49%
8: 2.26%
7: 3.26%
6: 4.58%
5: 6.44%
4: 9.23%
3: 13.68%
2: 23.15%
1: 51%
As you see, getting the ace 1 out of 13 times represents the normal chances of an ace and represents a standard house edge on a game. Getting the ace every time gives you your 51%. It's also obvious that you have to get the ace at least 1 out of 9 times before ace sequencing becomes competitive with counting as a choice of how you are going to spend your time in a casino.
What many sequencers have forgotten to take into account is what happens to your edge when you don't get the ace. If the dealer looks at your first card, puts it down and says "This card is not an ace, do you still want to play?" your answer is 'No' because your average edge when you don't have an ace is around -4.7%.
