you have to pay a premium to hire the use of it and then pay it back. Pretty basic I know but it is never explained that way.
Yes you have to pay a premium to use it - interest rate. BUT if your return on the investment you are making with OPM is greater than the interest rate you are paying - then waht is the issue. You are in front.
And NO - you don't have to pay it back. This is a common misconception. You can do IO forever and a day. The lenders do not want the money back - they want to earn the interest by lending it to you. The last thing they want is for you to repay the loan.