Actually a blackjack will occur closer to once every 21 hands. To be more specific in a six-deck game the probability of a blackjack is 2*(4/13)*(24/311) = 0.047489. An extra quarter this often is worth 0.25* 0.047489 = 0.011872. Divided by the $2.50 bet this adds 0.004749 to the player’s expected value. Most games where the dealer stands on a soft 17 or uses 1 or 2 decks will have a house edge less than this. So, yes, you could gain a small edge. Assuming six decks and dealer stands on soft 17 the player’s expected profit per hour, based on 100 hands per hour, would be 16 cents.