This is a great fly if you don't plan to be in a storm. That may sound stupid, but the fact is most Yosemite and Zion climbers never count on a storm. Ninety-seven percent of the time a storm never comes and they are fine. Three percent of the time a storm comes and causes massive suffering, rescue, and death. So this is a great fly to at least save you from rescue and death (you may still suffer). You can set up the fly above the portaledge so that if rain or snow unexpectedly comes during the night, you can drop the fly. It is relatively affordable compared to other rain fly options like the Black Diamond Deluxe Cliff Cabana Rain Fly and the Metolius Bomb Shelter Rain Fly.
If you are climbing when a storm is likely or in winter, we highly recommend the Black Diamond Deluxe Cliff Cabana Rain Fly. But for most Yosemite and Zion climbers, this is a great option for a "just in case" rain fly.