The bottom line: The Rab Storm Gloves are comfortable, warm, windproof, waterproof, and relatively inexpensive. Though the synthetic construction is less durable and grippy than a leather glove, it cuts down on weight and cost significantly. For winter activities down to 0F, they'll keep your hands cozy.
The Rab Storm Gloves are waterproof, insulated gloves intended for use in cold and wet environments. They have non-removable fleece lining, which makes them extremely soft and comfortable to wear. They also use Pyrotec insulation to keep your hands warm.
I have used the gloves while hiking in roughly 10F conditions, and they kept my hands warm. They are intended for use in temperatures down to 0F (-18C). Depending on the size you order, you may also be able to wear thin liners with the Storm gloves, which will increase the warmth further. If your hands do get cold wearing the Storm gloves, the palm area is loose enough to pull your fingers into a ball - however, the fit will vary between hand sizes, of course.
The gloves use a non-adjustable elastic wrist cinch and an adjustable gauntlet cinch that's easy to use while wearing the gloves. They have a hanging loop on the middle finger, and also a small clip to attach the two gloves together.
The Storm gloves are waterproof. I tried running water from the faucet directly over the gloves for several minutes, and my hands stayed dry - however, the outer nylon fabric does wet out fairly quickly. The waterproofing is provided by a Porelle Dry layer hidden underneath the ripstop nylon shell. I also have used the Storm gloves on warmer hikes putting my hands in wet snow repeatedly, and the gloves kept my hands dry.
On warm (~30 degree) midday descents I found my hands getting sweaty inside the gloves, suggesting that the breathability is not ideal. However, Rab only recommends the gloves for use under 20F, so it's expected that warmer temperatures would lead to sweaty hands. In my opinion this problem can be avoided by selecting the right gloves for the temperature - using liners with the Rab Storm is a great option.
The Storm gloves offer fairly good dexterity and grip due to the goat leather palm and thumb. The fingers have the ripstop nylon outer shell, which is less grippy than the leather areas. I found this a bit annoying in certain more critical moments with an ice axe, but the leather palm and thumb still gripped enough to avoid slipping.
The nylon exterior of the Storm gloves feels solid, and the seams are tough and durable. The leather palm also aids the durability in the areas of higher wear. These gloves will never be as durable as a full leather glove, but they are significantly lighter at around 150g (full pair, size L), and I still expect them to last several years.
At $60, I think the Rab Storm gloves are a good value for a warm and well-made waterproof glove. There are so many glove models today that it can be hard to choose - but Rab is a high-quality brand that does not disappoint with the Rab Storm gloves.