According to expected utility theory, it is, and this seems right (setting aside risk aversion). What does a knowledge-action account advise? Well, that depends. Consider two possibilities:
1) You are certain that the coin is fair, so you know that the objective chance of heads is .5. You can use the fact about the objective chance as a reason to take the bet.
2) You have no idea whatsoever about the bias of the coin. Using the principle of indifference, you assign credence .5 to heads. What knowledge do you have that could makes it rational to accept the bet? (Hawthorne and Stanley don't want to allow knowledge of subjective credences.) If there isn't any relevant knowledge, then it's not rational to accept the bet.
Here the knowledge-action account seems to makes a distinction between the two cases that expected utility theory does not. This is worrisome for the knowledge-action account.
Note: Expected utility theory will distinguish between the two cases when you're allowed to acquire additional evidence first. But that's not an option here.