A loose tether may become entangled in the Rope Wrench causing the device to 'lock' in a neutral position.
When load is applied in the locked, or inverted position, the Rope Wrench can be dragged down onto the friction hitch causing the knot to release its grip from the climbing line.
ISC and Singing Tree have made a concerted effort to answer all the critics by covering everything from installation to set-up, operation and maintenance of the ZK2 Rope Wrench.
Details including climbing line diameter and the length (and style) of the friction hitch are listed but, interestingly, there is no mention of the length of the stiff tether.
Surely this must be an oversight by the authors.
Since the stiff tether is sold as an optional extra, climbers new to the Rope Wrench often ask what length the tether should be (possibly with a view to constructing one for themselves?).
The ZK2 instructions do list the commercial availability of stiff tethers and Treetools can tell you the commercial 'stiffies' are approximately 300mm long.
There is still some debate in tree climbing circles about the optimal length of the stiff tethers, with some climbers preferring them slightly shorter than 300mm while others say they should be longer.
Designer/manufacturer confirmation regarding the length of the stiff tether would be the preferred option.
That niggle aside, the new ZK2 instructions should be a great step forward for this controversial SLWP device.