The biggest disadvantage investing in bitcoin is because the price is already very high and to reach huge winning rates like in previous years is almost impossible. Therefore it is clearly a better option to invest in other and low priced altcoin projects with the potential of highly increasing prices and winning rates. For using bitcoin as a payment method the current price is of course irrelevant.
It is actually funny when people are talking about the disadvantage that surrounds bitcoin where as someone disadvantage can actually be someone else's advantage.
I use to think of the high fluctuation as a disadvantage anyway, but with some trading knowledge, I was able to switch that to be an advantage for me. Everything for me so far has been advantageous; easy transactions without a third party, I can easily make my own decisions without the interference of bank policies, my asset keeps increasing and I can easily trade it to even make more.