An X flow means single pass...the liquid flows along the length of the rad once, from one corner to the other corner diagonally. Its less restrictive but the heat transfer would be less
Note that the inlet and outlet would be on different sides of the rad

A standard BIE is 2 pass...the liquid flows from one side to the other along one set of tubings, and then back to the same side along another
More restrictive, more cooling and both barbs are on the same side which may or make not make life and tubing routing easier