DMM
Ultra O Locksafe v1b

Identical to v1a except for laser markings on the spine. These differ in size and order of the marking information.

In practice, the Locksafe autolocking mechanism feels like a typical lift-and-twist triple-action (double-locking) carabiner, but it does require the sleeve twist to occur before a lift can be performed to permit the remainder of the sleeve rotation. This makes the mechanism technically quadruple-action/triple-locking (twist-lift-twist-open) but in practice I am already applying rotational pressure even before trying to lift the sleeve (often with a bump against my side or another piece of gear). Since both twist steps are in the same direction, this additional step is hardly ever felt in use - unlike the DMM Ultra O Durolock.

Like typical lift-and-twist carabiners, I have been able to accidentally open the gate by pressing the carabiner gate against a tensioned rope.

Locking oval carabiners are very popular with tree climbers for use with a closed friction hitch or mechanical friction hitch (such as the Akimbo or Rope Runner). The oval shape loads consistently and minimizes crossloading or carabiner rollout - making them ideal for connecting to rigid hardware such as hitch tending pulleys or modern mechanical hitches.

The availability of multi-attachment hitch-tending pulleys such as CMI's RP141 shifted production DRT (MRS) climbing towards more compact carabiners to clean up attachments at the saddle. The parallel side-plates (cheeks) of Treemagineers' Hitch Climber Pulley took up little space on the carabiner, overcoming one of the main disadvantages of oval carabiners and ushering in the modern era of locking ovals.