The DMM Boa is our favorite large locking carabiner. It is easy to handle, burly and holds a lot of ropes and slings. It is easy to clip to a harness and very strong. It's also a great all-around locker for winter due to its large size, which makes it easy to handle with gloves. It's not great for multi-pitch or mountaineering if weight is a factor smaller biners that may be a bit harder to handle with gloved hands may be better for a certain situation since they are lighter and less bulky. If you want a less bulky biner, try the Petzl Attache, Wild Country Synergy, or Mad Rock Ultra Tech HMS. The other comparable locking carabiners (as far as size and weight) are the Omega Pacific Jake, Black Diamond Rocklock and the Petzl William. If you are on a budget get the Rocklock; it is half the price and scored great. Otherwise, if you are going to spend close to $20 for a locking biner, it's hard to beat the Boa.
DMM Boa Review
Compare prices at 2 resellers Pros: Smooth gate, holds lots of ropes, good gate clearance, light for its size
Cons: Bulky and heavy.
Our Analysis and Test Results
The Quicklock gate is a great belay and rappel locking carabiner because it is so, well, quick. If you are taking it on and off a lot it is faster than a screw lock. This biner has lots of space for multiple knots or slings, making it great for belays. It scored well but not the best for how smoothly the rope pulled through it. We loved the keylock gate design that minimizes snagging. It has great gate clearance for easy clipping and works well with a munter hitch. It is an ideal locking biner for winter because it is one of the largest pear-shaped biners on the market. That makes it easier to handle with cold, gloved hands. The colors, I-beam construction, and twist-lock gate make this one of the cooler locking carabiners. For its large size it is relatively light compared to other large lockers. Lastly, it just feels secure, which gives you extra peace of mind when stepping off an edge on an exposed rappel.
The only dislike with this locking carabiner is how heavy and bulky it is. If you have a couple of these clipped on the side of your harness, you notice it.
This is a great belay device locking carabiner or all-around locker. We found it was one of the easier ones to operate with gloves, which makes it ideal for winter use. For belaying we liked the twist-lock gate version the best. The screw-lock gate is also effective, but we feel it is better suited for an anchor or backup biner.
This is one of the more expensive locking carabiners, especially with the Keylock (aka twist-lock) gate. That said, if you buy it as your main belay carabiner and you use it a ton, it's a good value because of its burliness and durability.
— Chris McNamara and Chris Summit