In reply to Oceanic:
Firstly you don't NEED a device specifically for crevasse rescue and it is always good to know how to do a crevasse rescue with the minimum amount of kit. However, mechanical devices can be useful and do improve the efficiency of a hauling system.
Having attended the same event that the Ex Engineer probably attended in switzerland for the last 3 years and i'm instructing on it again this year. There are many BMG's who assist and provide training and info on kit and systems. From this I chose to go with the Kong Duck, which at the time was better than the wild country rope man equivalent, which i now believe they have modified so that it is pretty much exactly the same as the Duck.
I don't always carry my kong duck, but i always carry a prussic.
It is important to note that whilst every effort is made to avoid dropping into a crevasse, it is inevitable that when something does happen, it will be in the worst possible situation and thus swift and effective rescue becomes more difficult. If a mechanical device helps alleviate some of the issues that can occur with the use of prussics etc then it is of obvious benefit.