Do you really want a 1/2 Flying, Deathtouch creature for 3 mana instead of a card off the top of your deck
In phantom drafts, if you win 50% of the time, you'll spend an average of $2.75 per draft, which is a pretty great deal for a couple of hours of entertainment
But trust me, the only ones who are going to make money off the McDonald's cards are the early birds, the ones who rush to market with a full collection or suspiciously sourced box of stock before people realize what a bad deal this is
Efficiency can be determined simply by the reward you receive at certain mana costs (Counterspell and Cancel do the same thing, but Counterspell costs less), the total payoff you receive from a single card (Hull Breach and Decimate are both good cards, but Decimate usually covers much more ground), or the payoff you receive in conjunction with other cards (Anointed Procession makes other token production cards completely absurd if unchecked, which is usually better than adding one more card that simply makes tokens like Spectral Procession in a token strategy)
If X is 4 or more, draw a card