The problem with locking climbing carabiners is the size of the screw (or twist, ball, magnet, pinch lock, etc). The lock must have certain strength to pass tests, so they are pretty big.

This is a problem when you combine these with the keysrings. If makes it very hard to slide the keyrings (with keys or other stuff on it) over the screw. This means you can only reach what is on top easily, but not the things below.

I really like the steel carabiners from the hardware (and sailing) store. Cheap, small enough to slide key around and build pretty strong.