First things first. Taking "even money" is the same thing as simply taking insurance when the dealer shows an ace and you have a natural blackjack (two-card 21). In both cases, you win the amount of your original wager, whether the dealer makes his natural or not.
Many players consider it prudent to take insurance on good hands, such as 20s and blackjacks. But unless you're counting cards and can detect a deck composition that calls for a departure from basic strategy, taking insurance is always wrong. What’s more, insuring the good hands is spectacularly wrong. That's because, in most cases in which you have a good total, some of the cards that the dealer needs to complete his blackjack are already out of the deck and in your hand. This is well-illustrated in the case where you have a natural. Note that the 10 in your own 21 is no longer available for the dealer to use, making it less likely that he will complete his natural. The casino advantage on insurance here, when playing a single deck, is a healthy 8.2%. The casino edge drops slightly when playing 2 decks, 4 decks, or more, but not by much.
Note that if you’re holding a 20 that's composed of two 10s, the situation is even worse. With two 10s now out of the dealer’s reach, insuring in a single-deck game affords the house a whopping 14.3% edge. Of all the insurance plays, insuring bad hands is actually the least damaging. Taking insurance with a hand made up of two non-10s, e.g., 9,7, carries only a 2% casino advantage. Still, that’s an edge higher than you face in many video poker games, on the bank or player bets in baccarat, or the pass or don’t-pass bets in craps.
So, yes, in a standard blackjack game, taking insurance can be defined as always being a sucker bet. But it wouldn’t be correct to say that insurance is wrong on all occasions. As mentioned above, card counters can detect situations where insurance is proper. Taking insurance can also be a powerful play during a tournament, where it’s sometimes used to maintain a lead over an opponent. And the basic strategy when playing with a matchplay or lucky-buck coupon is to always take insurance, regardless of your hand.
