This is a quick look at the Cardshark folding knife. Purchased this for less than $10 on sale.
Some things I like about it:
Lightweight - weighs ~14gms
Fits perfectly in your wallet due to its credit card size dimensions.
Durable (so far) - I've carried this around in my wallet/pocket and so far no damage done to it.
Easy & safe to use - it has a lock for the blade so it doesn't accidentally flip on the open position. It turns into a knife in 4 motions - unlock safety, flip blade, fold smaller portion, fold large portion over that which clicks it into place.
Price (see above) - good for the budget conscious.
Some things I don't like about it:
There's only one actually - The final fold of the large portion to the smaller one doesn't always stay in place. After a couple of times, it pops open so you end up having to readjust your grip on the handle to keep it locked.
Here's a caveat: This knife might be awkward to handle for those who have really big hands.
For what it is, it's not too bad of an investment as far as having a knife with you for general purpose only.