Basically, a Bitcoin ETF is one where the underlying asset is Bitcoin. This means that when you purchase Bitcoin ETF, you’re purchasing the cryptocurrency, albeit indirectly. This is because you’re holding the Bitcoin ETF in your portfolio and this ETF tracks the real-time price of Bitcoin. Therefore, the difference is that when you invest in Bitcoin ETF, you have the luxury of trading Bitcoins without the struggles of buying and storing it.
that's the biggest problem though. when you buy something like Gold ETF it makes sense because you can't buy gold ingots and store them in your garage. it takes a lot of space and it is dangerous. but when we are talking about bitcoin, storing it is not a "struggle". it is in fact one of the easiest things in the world while reaching the maximum security. for example for average Joe who doesn't want to bother learning anything they can easily buy a hardware wallet which is basically a tiny USB-disk-like device and store it there. and for those who want to make an effort you can simply create an encrypted paper wallet and store bitcoin there.
this is one of the reasons why i still don't see the point of bitcoin ETF!