I did have otos, snails, amano shrimps. They are all algae eater they were eating algae. But I always had to clean the tank myself regularly despite this. If there is an algae outbreak, they will not clean the mess, snails may reproduce in response to algae outbreak, but it takes them too long to adjust, so anyway the tank keeper will have to do something himself.
I never saw anyone of them eating filamentous algae, maybe some snails on the filamentous, eating some, but at best it is only reducing filamentous algae growth a little.
I never saw any of those touching cyanobacteria.
They are quite selective on what they eat, one day they may feed on flakes fallen on the bottom, one day they may clean a glass of it's algae, for example cleaning the left glass, leaving the algae on the other 3 glasses, and then don't touch them for 2 weeks, and go cleaing a root or some echinodorus leaves instead. Even so, they had to habit to leave a lot of algae on the echinodorus leaves, the algae continues growing and the otos can go regularly snacking on those. It's like they do it on purpose to have some algae reserves to snack.
I had to share my little experience with them, they help, they do not do miracles. One day I purchase 4 otos and they clean almost completely my 20 gallons of diatoms, then filamentous algae arrived and they were not touching that algae at all, and then the otos must have been starving in the pet shop, they ate like pigs the first week and after that only little algae.
Maybe algae eaters should be acquired because we love them. Not to have them as mess cleaners, which they do only if they want and when they want and what they want, one maybe grazing on a diatom algae for example and ignore completely and other kind of algae. Then you may want to stock different kind of algae eaters hoping that the mix will attack all of kind of algae but there will always be some kind of algae left untouched.
Plants and algae grower.