No matter what model/algorithm you use, it's not reliable enough if all data you have is only past Bitcoin price. Without external data (such as sentiment about Bitcoin on twitter or latest news about Bitcoin), i expect people who use that model/algorithm could go bankrupt when something big happen (such as an exchange hacked and most funds stolen).
With the help of RNN the network can be predicted but it doesn't mean that the outcome will be correct at all time. The previous bitcoin price performance is the external data that will be used. However, RNN is compatible with speech and language or any sequential input. The bitcoin price can now be determined using the LSTM to keep track of the already saved prices inside the memory.