The Black Diamonds Dynex Runner is a super compact and lightweight option for the light and fast traditional climber, or those alpine ascents. At 10mm wide they are a full 8mm thinner than Black Diamonds nylon slings. They are also significantly thinner than some of the Dyneema slings that we tested. Due to a super tight weave, these slings garnered a top spot in our durability rankings exhibiting minimal fray throughout our testing, assuring a long life for these slings.
One of the best things about these climbing slings is also one of the biggest drawbacks: the 10mm width. While the skinny sling saves you a bunch of weight and bulk, the thin width also makes it extremely difficult to untie a knot that has been weighted. After weighting a nicely dressed overhand knot, we (not having any fingernails) actually needed pliers to untie the knot. We also found that the thin width of the sling lends itself to tangling a little more frequently than slings of a greater width.
Another drawback to these is their price, which is significantly higher than a Black Diamond Nylon Runner. Also, while the sling technically works as a friction knot or rappel back-up, due to the low melting point of Dynex, we cant recommend that the sling be used in this way. The friction of the rope on the sling can actually melt the fibers of the sling compromising the safety of the system.
Black Diamonds Dynex slings will be best suited for situations where low weight and low bulk are the highest priority. Speed ascents, alpine ascents, and long traditional routes are scenarios where you'll be thankful to have a set of these on your rack.
There is a good discussion about Black Diamond Runners here http://www.supertopo.com/climbers-forum/1245623/BD-Dyneema-slings