I'm about to consider opening one myself in advance of starting to receive Social Security - that way I don't have to play the exchange rate game. Hopefully it will also allow me to make the annual payment to the IRS and hopefully receive stimulus checks!
Would be interested to hear of anyone has gone this route....
Given that SS will be taxed in the UK (assuming you pay on the arising basis), you are generally better off having it paid into your UK account. The Fx rate is the best available "on the day", which is the 3rd of each month unless the 3rd falls on a weekend or holiday. You also know exactly what to declare on your UK self-assessment, since the instructions for the SA stipulate that the Sterling amount is calculated on the date the foreign income is received.
Retaining a US account is a good thing for many reasons, but make sure you link it to your UK address, not the address of a relative in the US.