Oto only get 2"max and have a different head shape. They also don't have the hard thick scales plecos have.
Just look and some photos you will get it. Also plecos eat everything they all like meat. But otos are plant eaters all the way. If starving they might try other meat like foods but given the choice it's plants. I have a few kinds of plecos and 2 otos. They are very different fish. Otos are by far the best algea eaters you can buy. They eat it all with out hurting plants.