I am not sure I understand the distinction between margin and cash accounts when it comes to safety in the event of a broker going bankrupt. Is this also the case for a margin account with no margin balance outstanding?

I have set up my taxable brokerage accounts with margin. I did this so that I could buy shares without having cash in the account. If the trade happens I transfer funds via ACH. Broker sweep accounts pay abysmal interest, so I keep no cash there. I have never actually had a margin balance, except once when I was assigned a short put while on a cruise and couldn't initiate a cash transfer the same day.

Also if I remember correctly I had to open a margin account to get approval to trade options. This was a long time ago, and I am not sure this is still a requirement.

Thanks.