i also don't understand, main reason is cos can't really zoom in to check more thoroughly.
Yes, that's the main reason I use it. If just shoot white oof bg at f22, I have to zoom in on the LCD and pan around to check for dust, which is slower and more troublesome than using dust alert. Dust alert doesn't catch some of the finest dust, but if it can't see the dust, the dust won't bother me either.