This is a great place to do work on your bike yourself. Not only do you save money compared with paying a mechanic at a bike shop or buying the tools yourself, but you get a real sense of empowerment from learning how bikes work and being able to repair them (or even build one) yourself. Especially for people like me who spend all day in front of the computer, it's a great way to get dirty and actually make something with your hands.
In my experience the volunteers are generally knowledgeable and helpful, if at times brusque. Get there a couple minutes before opening times if you want to be sure to get a bike stand, otherwise you may need to get on the waiting list.