I do use leverage in one of my strategies when in “crash recovery mode” and in another strategy I use it constantly with a different multiplier depending on the state of the market. IBKR has the cheapest interest rates as mentioned.
My strategies are mechanical and checking the margin in real time is part of it. It is quiet easy done in a spreadsheet. Details I did describe in my “mechanical investment” thread:
A word of warning: without leverage you have a “stress tolerance” of 100%. That is how much your equities can fall in price. When using leverage you have to define an emergency exit where to sell and this must be way before your broker starts selling or issues a margin call.
At this point you are obliged to sell at the worst possible moment: when stocks are down!