Originally Posted by BillyTB

It was free for one year when you switched from the M&M Amex to a regular Amex. Not sure if there were limits (I had the “premium” M&M card)… It would be free for gold and platinum cards (and a paid option for other cards)… My assumption was that this was needed to at least keep the mileage gains identical.
There is no mention of it on my statements, but the math checks out