I have a Rainford. Doesn't eat anything but tiny strands of hair algae. I didn't get him to control hair algae, but for the fish he is. My tank is BB so I can't comment on sand sifting, but on occasion he will grad a mouthful of something, maybe detritus from a rock and sift it.
One thing I was shocked to see, and again, he wasn't brought for this purpose, is he will grab and eat cyano from the water column if I brush some off. And when I say he grabs it, I mean he will attack it and swim all over with it hanging out of his mouth. I don't have any problem with cyano, just every so often a tiny patch will show up.