I would guess that the decision of which GiveDirectly programme to support† is dominated by the principle you noted, of
the dollar going further overseas.
Maybe GiveDirectly will, in this case, be able to serve people in the US who are in comparable need to people in extreme poverty. That seems unlikely to me, but it seems like the main thing to figure out. I think your ‘criteria’ question is most relevant to checking this.
† Of course, I think the most important decision tends to be deciding which problem you aim to help solve, which would precede the question of whether and which cash transfers to fund.