This gadget is okay but I am not sure it adds a huge amount of utility to what I would deem the traditional type of slicer that my mum used to use.
It features a blade at the top, which enables you to chop the ends off of the beans. The beans are then passed through a sliding spacer into more blades that both strip the edges from the bean as it passes through and cuts it into strips as you do so. If the bean is stringy or too wide, it won't go through the mechanism - the traditional slicers stop stringy beans but are able to cope with larger beans than this slicer.
I found it a little tricky to use initially, but I soon got the hang of it and I ended up with nicely chopped beans in a short amount of time. I suppose the integral blade to remove the ends helps speed up the process, but you can achieve much the same using a knife (it just takes a bit more time) and I never was all that bothered about removing the edges. I suppose it is okay, but I'm sentimental and would prefer to use my mum's traditional slicer instead - if I hadn't given it to my sister.