If to evaluate this gambit formally it seems to be somehow risky, while further analysis shows that the position of Black is stable and favourable. It is clearly playable for Black and a lot easier to learn than the huge "normal" lines.
Having in mind the effect of surprise, it can bring you valuable victory in a crucial game. In addition to that, you take over the psychological initiative at the first moves.
Instead of the usual long defense in the Queen's Gambit - Orthodox Variation, you bravely counter-attack as soon as at the fourth move.