The Rescue is made to work with ropes of diameter 7mm to 13mm. As the name suggests it it made for heavy loads, and the large diameter ball-bearing sheave is very efficient. This is one of the makes of pulley considered suitable for use by Speleo Secours Francaise in their counterbalance system, which is detailed in the Cave Rescuers Manual.
This is probably 'overkill' for personal use - although it is not particularly large or heavy - but is certainly appropriate for instructors, or as part of an expedition rescue kit.
Weight 185g. Efficiency 95%. Working load is 8KN; breaking strength is 36KN.