I just discover one limitation. That is, while they are designed to clip into metallic clips and anchors up to 12.7 mm dia., they do not recommend connecting directly to rope. They are perfect for fastening into the rungs of a guyed tower, which is why I like them.
They also don't recommend working loads over 1/4 of the device rating, but this may be typical of other comparable devices. Still very quick, easy and useful.