How does the interest work?
9% a year on ameritrade, you will get a margin fee every month depending on how much margin you are using. you need $2000 minimum and you cant ever let your stocks+cash be less than that
but it works good, cuz if you go to an atm your debit card shows your cash + your margin as the amount available, so you can have access to your margin anytime.
td ameritrade checking + brokerage is a really really good combo IMO, I think the best part of it is that when you get extra cash you dont have to ask whether you should spend it or invest it. the answer is simple, you invest it and then use the margin to spend on what you want