I needed a new 5mm allen, so I thought I would give this a try since there are so many 4,5,6 sizes when working on bicycles. It is good quality, but I find I can't spin it as the other sides get in the way. I don't use it as much as I thought I would.
Having been both a bike mechanic (home and professional) as well as an avid cyclist for many years, I can honestly say this is one of the most important tools for anyone who rides a bike to have in their home toolbox. If you're making adjustments, its' very nice to have the three most common hex key sizes right there handy without having to fish around in a toolbox. If you're toolbox is as messy as mine, that can be a bit of a frightening undertaking!