Pros
You have freedom* to set your own hours. *It comes with the understanding that if you don't pick the hours they hire you for, then you won't have your contract renewed. First lesson of OE: don't take what they say at face value, because you will lose your job if you do. More on that in the cons...
Cons
If you want to understand the OE mentality, all you have to do is read the comments recently posted by the company trying to boost its image...then compare that to what people from all levels within it have written about the serious problems. OE will indeed lead you on, use you up and then fire you (without warning, even) to hire someone cheaper to do your job. This is always regardless of quality, regardless of commitment. I repeat -whether you are a student, teacher..whatever. You are simply a number to be crunched, in the eyes of the management. If you ignore what so many people have written here, you do so at your own risk. It goes without saying that there is no job security. But even worse, it seems that they have intentionally made it more and more difficult to even find the right person to contact, if you have a problem. I am so sad to see that the company I used to be so proud to work for has turned into this.