I have not found any specific information about this species in the fly fishing literature, but I did encounter a spinner swarm plentiful enough to make for great fishing in the right kind of stream. However, this was happening at dusk in a stream where the biggest trout were seven inches long and they would all charge any dry fly that hit the water, hatch or no hatch.
I observed a swarm of thousands of Cinygmula par spinners gathered over a riffle at dusk on a small stream on the east slope of Washington Cascades on July 4th.
Pictures of 3 Mayfly Specimens in the Species Cinygmula par:
It's remarkable what thick hatches, and especially spinner flights, can come from a species few anglers have ever heard of. The genus Cinygmula is thought to produce unremarkable spinner flights, but this one would certainly have gotten the trout going if it weren't happening just before dark on a small stream where there isn't a lot of nocturnal feeding.