The Black Diamond Fifi Hook is a solid fifi hook that gets the job done. I've used it on a lot of El Capitan ascents and felt it works well. It's one of the lighter fifi hooks I have used. It is also one of the few fifi hooks to come with the runner pre-sewn in. That saves a little time and is nice if this is a last-minute purchase before a wall and you don't want to bother finding some webbing.
It comes with a little hole on top so you can rig more advanced solo hauling systems. I won't explain it here because, to be honest, it's something I pretty much never use. But if you want that feature, this has it.
Because it is so light and made of aluminum it's not the strongest fifi hook. A heavier steel fifi is more burly. If you pinch it between a bolt hanger and a biner and torque up, it is possible to bend it. If you take a daisy fall onto it, it might open open up. This has only happened to me once and is not a big deal. Most people will never run into this issue but it's something to be aware of. One downside to the pre-sewn runner is that it probably will not be the exact right length. If you are tempted to use it at the improper length, DON'T! If the fifi length is not perfect, you should cut off the webbing and buy some webbing to make sure the length is perfect. How do you know what is the perfect length? Check out this article from my How To Big Wall Climb Book. Personally, the runner is a little too long for me so I cut it off.
This is ideal for all aid climbing applications.
It's the same price as the Petzl Fifi Hook. I don't know of too many other widely available fifi hooks.