The Metolius FS Mini 2 carabiner is one of the lightest and smallest climbing-strength carabiners on the market. At first, we thought it was a keychain biner — it is that small. It is much smaller than the Black Diamond Oz. It is also lighter — 23g compared the Black Diamond Oz Carabiner at 28g. The CAMP Nano 22 Carabiner is just a bit lighter and is a little bit bigger, making it a better choice if you need something that handles a little easier. That said, our tester still find the Nano to be quite difficult to use.
The Black Diamond OZ, Wild Country Astro and Mad Rock Ultra-Light are all 5 to 10 percent heavier but also easier to handle. I find that overall the few grams extra of those three biners is worth it for having a biner that is easier to handle. However, the OZ is more expensive. Only the Mad Rock UltraLight Bent Gate is significantly less expensive and it is also a bit heavier. It's a tough call with so many great light biners available.