Buying Bitcoin ETF vs Buying Actual Bitcoin

I apologize beforehand if my knowledge of ETF's is lacking.

First, my understanding is that an ETF is much like a mutual fund, where it mirrors or tracks the value of the underlying asset (in this case - Bitcoin). If the value of Bitcoin goes up, the price of the ETF share goes up and vice versa.

Second, my understanding is that this would be aimed at "traditional" or "retail" investors, allowing them to have exposure to Bitcoin.

Third, this is all assuming perfect world scenario's where the Bitcoin ETF(s) get approved in the US.

So my question would be if I had X number of USD, is there any difference between owning $X Bitcoin ETF's vs owning $X of actual bitcoin which would be stored in my wallet with my keys?