up/down systens are stupid since they are so binary. It only remotely works to give you an actual picture of what people think about it. Having a five scale score is very logical, since it's symetric (and therefore not biased like the 6 scores rating you suggest if you could rate without stars), and you give a degree of satisfaction and not just up or down. It's way superior to tell you if the product is exceptional or just "meh".

Of course you have to look at the ratings distribution and not just the average. The average tells you almost nothing.