Well made. A couple of flaws.
Not being able to see the last card on top after the thirty seconds is a HUGE problem. Often I will click for a new card as soon as the time is up and it takes the new card into account, even though I didn't see it, or if I did it was for a fraction of a second, ruining the test. Also not giving a sound que or visual que for a new card that is the same as the one before it often gets me mixed up because I think my tap didn't register leading me to skip a count.