The Kong Resting Fiffi is also known as the "adjustable fifi" because you can rig a system where the fifi length is always adjustable. To do this, you need to buy 6mm accessory cord separately and spend a little time figuring out the system. I have not seen too many people climb efficiently with this system but there are others who swear by it, so you might want to check it out. This is one of the lightest fifi hooks and is also the cheapest one. The fifi hook I prefer is the classic Kong Fiffi Hook. I prefer it because of the standard "non adjustable" setup and the fact the hook has a larger opening. In the little I have experimented with the Resting Fiffi I have found that the more open hook design means you have to be more careful about the hook coming off your biner unintentionally.
PS: I don't know why, but Kong spells fiffi with two f's whereas everyone else spells it with one f. Keep this in mind when searching for this product on the Internet. — Chris McNamara