You cannot transfer to a friends US account, only to another UK account.

These bonuses are becoming more regular, one or two a year, but they are targetted.

The trade off, for you, is how long you want to pay the £37 per month Plat fee before cancelling.

What you could do is get an Amex Gold card for yourself (fee free for first year) and then cancel Plat. Your MR points are secure because of the Gold and you then have a years grace to use them during your Gold fee-free first year.

Even better ... refer your partner for a Gold. You get 12k for referring, he/she gets 22k for being referred. You can tehn pay the £15 fee to transfer your 50k to your partner and cancel your own Plat. When a bonus comes along, you move them to your partners BA account.