When the ProShares Bitcoin Strategy ETF debuted last week, it received a rush in inflows, making it the fastest ETF to surpass $1 billion in assets. However, according to JPMorgan, the futures-based ETF has a major fault that might result in poorer returns for investors if the fund’s assets grow too large. This is due to the fact that the ETF’s underlying asset is not bitcoin. Instead, the ETF owns bitcoin derivatives that use futures contracts to try to mirror the cryptocurrency’s return profile. Gary Gensler, the chairman of the Securities and Exchange Commission, has resisted requests for the SEC to approve a spot bitcoin ETF, preferring instead to approve a futures-based fund.