I currently have a 5 gallon cherry shrimp colony tank that had an outbreak of black brush algae. It was recommend I buy a zebra nerite snail, so I did. Well, he ate a little bit of it but not down to the roots. But within a day he had completely scraped off all of the regular green algae that was starting to grow on my rocks and driftwood. I didn't necessarily mind that algae, but the fact that he had All of it gone in a day tells me that they're good algae eaters. I imagine that in a tank with a ton of algae on the glass the nerite would be best.
I kept amano shrimp before as a kid. I tossed two in a neglected ten gallon about four times overstocked with platies and which was completely overrun with regular green algae, so much that every wall was covered and even the front pane was pretty funky. Coincidentally, these guys are very, very hardy. In the ten years that tank had been set up it had had 3 water changes, all in the first year. The nitrate was no doubt incredibly high and they still lived for a few years but eventually jumped out. Anyway, it took a year, but eventually they had the glass about two thirds clean and much improved, and then they didn't clean it anymore. I think that once they had eaten up that much algae, there was nothing left to let them cling to the glass so they couldn't eat any more. But they maintained it at that level. They completely cleaned the ornaments of algae as well. I find them worth keeping just because they're interesting little animals.
I only kept otos once, and they lived for about three hours, so I can't speak much of them.