I asked on here about that very advert the other day, when someone said that a pic was a CAE and got massive.
Several respected and experienced members, said that there was no such fish as a dwarf Algae Eater and that it was just a sales ploy. I couldn't tell you if they were right, just that I trust their opinion.
When I said 'Very' I meant very common, P@H have them although they label them just 'Algae Eater' They are £1-£2 something like that. This is why I said 'cheap'. If you read the description in the Fish Index you will see that when they get older they will develop a taste for fishes body slime and eyeballs.
I've never had one and am not likely to get one so I do not speak from experience, just what I've read when researching before I buy for my own tank.