the biggest disadvantage is: inflatory i.e. speculative nature that brings rich people mixed in bitcoin and they can pay 1000 slaves to make fictive demand at different exchanges and change the value of bitcoin.
they can buy 100 bitcoins for 400 Eur and make small demands with high prices (1000 x 0.0005BTC for 10 Eur, for example), then the value of BTC will jump up and they will sell 100 BTC for 1000 Eur per BTC. then they let the value to fall down, to buy BTC again, and again they make many small demands on the market to push up the value of BTC.

in any case, we can be all agreed that rich predators are mixed in bitcoin already 2 years and even their regulation efforts are bad for ordinary people who don't have 100 000 eur to pay for the license to be legal BTC exchanger in Luxembourg. to become BTC exchanger, it will be hard as for example to get a license for casino. only rich people can get it, nobody else, it means, there will be monopoly who will become legal exchanger.

beside speculative nature of BTC that attracted predators and 1000 slaves to make masters richer, second biggest disadvantage is the topic called exchangers.
centralization of BTC by exchangers, NSA exchangers (coinbase), and now even regulating bitcoin by the law will allow to predators to have monopoly who can become an exchanger, only those who pay big money to the state.