To be honest, I believe that it is definitely impossible to answer whether BTC is legal. On the one hand, it is kind of legal, since many countries do not prohibit its use. On the other hand, if we talk about BTC as money, then it is not legal, since there are countries that prohibit the use of surrogate money. Based on this, it is impossible to answer 100% whether BTC is legal or not. The most you can do is find out in the country where you live, how they treat BTC at the legislative level. As far as I know, there are still discussions in the world about what cryptocurrencies are and how to identify them in the world system. Moreover, every time something changes in this regard, which means you need to learn more information.