They do eat algae; while young. They can (but rarely do) grow to 11 inches. As adults (5+ inches) they rarely eat algae and perfer flaked foods and bloodworms. They can be VERY agressive and have been known to attach themselves on larger slow moving fish, (Oscars) sucking away at the slime coat, eventually penetrating the skin and killing the fish. (Wow that was a fragmented sentence if I ever type one!)
My LFS sells them as a Golden Chinese algae eaters. They will eat algae when younger but as they grow they will eat less and less and become more and more aggressive. I had one take a chunk out of my Gourami that later died, so beware.
my sister in law had one of these in her tank...it was a large 4-5"er. It actually did a very good job at eating diatoms and didnt bother the other tank inhabitants...it didn;t however touch the other types of algae. ..it was like a big oto in that regard LOL