The Walton original is a brilliant creation that is extremely strong. The weakness of the effect is that the deck is spread face up prior to the production of the mentally selected card. In truly expert hands, where there is no hesitation and the performer's attitude is that he is merely displaying the cards, it is a stunning effect without any solution.
Executing the cull while projecting this attitude -- and making the whole thing feel unstudied -- is extremely difficult...rapidly finding and culling the card while convincing the spectators that nothing has happened is one of the most difficult tasks in card magic (this is why "think a card" is almost never performed well)...far more difficult (and far more important) than memorizing a deck, becoming an expert in estimation, or performing an imperceptible pass...
By having the deck spread face-down the deceptiveness of the effect is dramatically increased for most performers -- and is increased somewhat for everyone...using darwin's method the performer need not even look at the deck...this makes the moment feel unimportant and renders it psychologically invisible...it is just a joke...
If the moment is not subconsciously invested with a sense of importance by the performer, then it becomes psychologically invisible (thanks to the great strength and weakness of the human mind: information that is irrelevant is destroyed). If we can succeed in making the first display psychologically invisible to the spectators, it will be deleted from their conscious memory. They will be left without any solution to the effect, and we have a miracle on our hands. If the moment of displaying the cards face-up, however, feels like more than just a casual gesture to accompany a joke..then we have a very clever -- even astonishing -- display of dexterity; but we do not have a moment of magic (that is, a moment of the utterly inexplicable)..
Darwin's handling does not guarantee a miracle. But, because it allows us to perform the effect without looking at our hands as we gesture, it means that those of us who are not David Berglas have a much easier time of performing the effect such that a spectator "does not suspect, let alone detect" the modus operandi. Darwin has helped us to eliminate a "dirty" moment.
It is a detail..but it is precisely these details that separate great magic from good magic.
Put simply, if you think that the memorized version is harder than the original -- then you probably are not performing the original well.