[TeMPOraL]

GiveWell is literally a priority queue of charities. The moment AMF starts getting diminishing returns, it'll drop down the list. If some other organization figures out an even cheaper way of saving lives, it'll overtake AMF on the list.

It's a simple and obvious system. I'd say the only two things to potentially quibble about is whether or not one likes their sorting function, and the lag time between resorting.