i've never had my cards fall out, but i'm gonna echo what others said and say that you can't stuff this piece as much as the cles!
depending on your keys (and whether you have a car key fob in there), it'll probably only fit 1-3 (at the very most) cards before it won't close comfortably. if you're looking for more of a catch-all piece for your extra cards/cash, i'd go for a replacement cles.
i personally use my 6 key holder every day and LOVE it, but it's up to personal preference! when i have to run out of the house really quickly and i don't feel like fussing with one of my bags, i usually just slip my license and 1 card in and call it a day.
edit: i'd like to add that maybe you could look into a recto verso cardholder for the best of both worlds! it comes with a little keyring like a cles, but you can definitely fit a larger amount of cards as well.