That is true, I’m a bit baffled they didn’t integrate this in some capacity into instagram itself. With that said I think this has a higher likelihood of success than instagram apps made for instagram users since this is an Instagram app using Instagram to launch a twitter replacement.
Fair point although I think “Hi there’s a new Instagram tab that is twitter” would be a more effective way to gain users than “go download a different app that you then have to log into using Instagram”