What is the difference between Bitcoin & blockchain ETFs?

Could you elaborate on the fundamental differences between Bitcoin and blockchain-focused ETFs? As a cryptocurrency enthusiast and investor, I'm keen to understand how these two distinct investment avenues vary. Bitcoin, as a decentralized digital currency, offers direct ownership of the underlying asset, while blockchain ETFs seemingly provide a more diversified approach to investing in the blockchain ecosystem. Could you explain the advantages and disadvantages of each, and how investors should approach these options? Additionally, how do the returns and risks compare between the two? I'm particularly interested in understanding the potential differences in liquidity and volatility.