Bitcoin only exists because it has been legally described as a commodity. And in a way that makes sense. Because bitcoin's value is rather uncertain and unstable. For it to really work as a currency it would need more stability. On the other hand there is no denying that bitcoin strives to be a currency. The original designer of bitcoin clearly wanted it to eventually replace currency, but with the benefit that it would be decentralized and take away the need for trust (which with money you have to place in a bank for example).
The problem is that if bitcoin ever were to be stable enough to be money, I think it is likely to become illegal.
Personally I wouldn't invest a lot of money in something that has such an uncertain future. But of course if you want to make big bucks, you can usually only do so precisely by investing in uncertain things.