I used to pooh-pooh flashcards. Making them was time consuming considering how long they were used. And then...I had a child who needed repetition. I found that having her go through flashcards with basic information (ex: addition math facts) each morning helped turn on her brain for the day.
Yes, we have used the standard homemade 3x5 index cards and the pre-printed multiplication flashcards. For homemade flashcards you don't usually need a full size 3x5 card, yet it is a pain to cut them in half. I have come up with what I think is a better way to do/store flashcards - a Rolodex. I copy questions from the science or history chapter we are studying and write the answer on the opposite side so that it is readable (upside down). It is as easy as reading the question and then flipping the card forward. No tracking down stacks of flashcards all over the house, they are in one place - on the Rolodex.
FYI, writing them out is still time consuming. I've also switched to blank cards.