Hand coordination
Not Mr D, but the reason I prefer a computer flash card program is that I don't have to worry about the hand coordination necessary to flip cards. I may be in the minority, but I find it difficult to flip a pack of cards, two at a time, in less than 25 seconds.
Also, some of the flash card programs will vary the rythm (time interval) of flipping the cards. This is something that you could do yourself, but then you would know when the rythm is going to change. This is a pretty useful drill since the rythm often changes in a real casino (dealer BJ, new dealer mid-shoe, etc).