Amanos live nice and long, and the best part is they get hungrier as they get bigger, meaning they eat more algae per day!
Unlike SAE which lose their appetite for algae as they age, amanos keep chowing down. My most recent import of amanos yielded 5-6 giant ones, which I added to my other 3 giant ones, and I can put any algae ridden decoration or driftwood in there and have them pick it clean in a day or two. They really like hair algae, and they're constantly picking the glass clean as well.
As far as dwarf shrimp are concerned, I had one CBS that lived just over 2 years.