The advantage of a margin loan is that the holder only exposes himself to fx risk of the pnl portion. The broker loans the purchase price/margin/...and that goes back to the broker upon liquidation. The difference is exposed to fx risk. Same as a house purchase on mortgage in foreign currency. The fx risk is not applied to the house value but to the realized pnl upon sale.
You have to do the math, but generally futures will have better implied interest rates than what a broker will give you, even IB. The question is, is it worth the extra risk/complexity/effort of rolling contracts, the extra margin use, etc. When I last evaluated this question, the answer for me personally was no.