Correction: they don't need to fly. They can be kept in a very short cage with no flight room. They can and will fly if spooked and trying to escape, but you don't need to give them room in which to do so like you do just about every other bird.
They're adorable little birds that make much better indoor pets than basically every other bird species currently in the trade. Mostly because they don't fly, and aren't smart enough to need much enrichment other than a few things to do.