The Black Diamond Oval carabiner scored highly in rope pull smoothness; when you run a rope though them there is less friction than with almost any other non-locking carabiner. This makes them excel for top rope anchors where two of them are used "opposite and opposed."
The one area ovals excel: racking pitons. Like a key chain, they allow pitons to slide around easily. That said, you could use two light carabiners for less weight and rack more pitons.
The solid gate Black Diamond Oval is incredibly heavy and bulky; over twice the weight of many wiregate biners. Got a big rack? You will notice a GIANT weight difference if you use a light wiregate instead of an oval. While they are good for racking pitons and slings, nuts get hung up easily on the unexposed notch, especially if there are a lot of nuts. The Black Diamond Oval is the heaviest we tested at 64g, yet the weakest at only 18kn closed gate strength.
Ovals are great for top roping or any situation where smooth rope pull is needed. It's not a bad idea to buy four to six of them when you first start climbing because they are cheap and you can learn the old school "carabiner brake rappel."
