Interesting that both these items have the "same" right-click spell but the specs are quite different.
Memory Flux from the Unearthed Belt is almost insta-cast (1/2 sec) but has a 1-min recast delay.
Memory Flux from Memory has a 5-second cast time but has no recast delay.
I spawned Grai in The UnderQuarry about 6x before he dropped the Unearthed Belt. This was an easy camp, probably took me 2 hours total. On the other hand, obtaining Memory is a long drawn-out process even at level 110.
Since Memory Flux isn't guaranteed to clear all aggro, the Memory version of it is far superior even with a 5-sec cast time. Figures, eh?