If it's complicated, you can be sure that it will work in favour of whoever wrote the terms.

I have one card that gives cashback. If I pay in full every month, there is no interest and the cashback (initially 1%, now ½%) is credited every few months.

I have another card that uses a lower interest rate than most cards but it charges interest from the date of purchase to the date of repayment. If I pay the statement amount in full one month, there would still be a litle interest to pay the next month.

My opinion is that, if the terms do not make sense, you should avoid them.