Something like.
1. It would be SEC (securities exchange commisssion) approved. Some degree of regulation would be involved which some believe to imply makes investments safer.
2. It could make it easier to invest in bitcoin, without having to buy actual bitcoins. A person might buy ETF bitcoin "shares" with usd or other currency.
3. An ETF could be leveraged. This means $50 invested in a bitcoin ETF could give someone $75 or $100 of bitcoin exposure, depending on whatever percentage the ETF is leveraged.
This isn't a complete overview of ETF's but suffice to say there could be some things about it that would make it more attractive to investors than buying actual bitcoins.