I honestly wouldn't bother unless you have unlimited credit card spend and can afford to throw some away on regular US card spend.Thanks for the advice - I think I'll have to give this some thought - the points earn with the exchange rate where it is, is pretty ordinary on the Bonvoy card but I think I'll need to suck it up if I want to get out of pop up jail.
US Amex business cards tend to have much higher chances of avoiding pop-up jail, so I'd try them if you're keen to acquire some more US MR.