Never use them, don't see the point other than as a table top tank at work or in a small apt. As far as fry tanks, I've always used larger tanks, usually 50 or 55. Fry tank doesn't need daily water changes that way. Never had cichlid fry unable to find food and I've raised thousands of fry, from new worlds to Africans, doesn't take them long to figure out where the food is. As far as space efficiency when you're breeding a lot of fry, I just use dividers in a larger tank to separate fry as needed.
Lot of ways to do things in this hobby, so not to be a know-it-all, and if you have a use for them go for it. But I don't use anything that small.
