Seth Ryanwrote a review of DMM Shadow Locking Carabiner on February 13, 2017
Familiarity: I've used it several times
I have appreciated the craftsmanship of other DMM products like their nuts. These locking carabiners are very light and as others have noted the locking mechanism is smooth.
I picked up a few of these for use in anchors. It would be too small for my taste in use with a belay device. But, for ascenders, anchors, and other places you want a locking carabiner these would be great.