Free Grace theology teaches that sinners receive eternal life the instant that they are certain of Christ's promise that guarantees their eternal security the moment they take Him at His word. Saving faith is taking Christ at His word wherein He guarantees the eternal well-being of all who simply believe Him to do so. Taking Christ at His word is certainty of one's eternal salvation, no matter what.
Saving faith is not accomplished by walking an aisle, raising a hand, filling out a card, praying a prayer, or confessing or saying something with the mouth. Eternal life comes the moment someone is certain that they possess eternal life through Jesus Christ in His promise, IOW, the moment they believe Christ.
There is such a thing as a false professor in Christianity. But it lies in only 2 areas:
a) One who lies and says that they believe in Jesus alone for eternal life (for purpose of infiltrating, or wishing to be accepted, etc)
b) One who believes a message that is not the saving message of Christ (the true gospel), and believes that he has believed the true gospel, and thus confesses that he has "faith in Jesus", which he does. But NOT in Jesus' promise that guarantees eternal life to the one who merely has bare faith alone in Him for it. He may have faith that Jesus is only one of many other necessities for final salvation.
There is no such thing as a spurious faith in Christ alone that has for its purpose the reception of eternal life. The modifiers, such as "head" faith, "false" faith, "spurious" faith, "temporary" faith, etc., are the machinations of those who oppose the idea that eternal life is, in reality, an absolutely free gift. No such modifiers to faith exist in the Bible. The Bible knows nothing of any such thing as a “substandard” faith in Jesus Christ for eternal life (not even in the Epistle of James or parable of the sower!).