Bitcoin rallied sharply in the past few weeks with the approval of BITO, the ProShares Bitcoin Futures ETF. Momentum is again Bitcoin's friend.More Bitcoin ETFs are likely to be approved soon, leading to increased investment demand for Bitcoin.With $12+ trillion in IRA assets in the US, even a small fraction migrating to Bitcoin could drive another upward surge in the price.Why I wouldn't buy the Bitcoin Futures ETF, and what I would buy instead for a ~18% return.