Thus I would say that the very popular NYKNYB phrase can be changed even to "Not your [Bitcoin] keys, not Bitcoin".
"Not your keys, not your coins" works well in the past, now and in future. When people know that this saying works, they will know about very big risk if they invest money in Bitcoin without access to private keys. If their investment choice does not give them private keys, they are doing risky invesment practice and Bitcoin storage practice.
Bitcoin Q&A: Not your Keys, Not your Coins. It's a video and takes time for listening but with this importance, newbies if want to learn can listen it.
If they want to save listening time, they can read this one.
Reminder: do not keep your money in online accounts.If it's regulated by the SEC, this all has to be disclosed. ETFs are, and it's fully disclosed as required by law. That can't be hidden.
There are always chances of abuse and if it happened with traditional banks, it can happen with ETFs. With my investment money, I don't want to trust any company to use my money for buying bitcoin, and give me something equivalent in return. I want bitcoin, private key to fully control my bitcoin, and don't want to trust any company for this vital task (bitcoin management with my money and bitcoin). If I trust them, I don't actually have bitcoin, and my trust can mean nothing for my Bitcoin fund safety.