What can I say, they keep your batteries together. They are light, the bare minimum needed to keep your batteries organised. They work really well, easy to push in and remove when needed. If they have one downside, they clearly aren't waterproof. So you still need to put them in a sealable bag or similar to keep water off your batteries. And for the small amount of plastic they are made of, they aren't particularly cheap at around £6 each. But they are available in glow in the dark plastic, but again, not cheap.
Are they worth it? If you want to store a lot of batteries I would look else where. For a few batteries for someone backpacking or hiking they aren't too bad. They also seem to be called Storacell by the same manufacturer.