From our review of a previous version, Rowi proved to be a winning client:
Rowi doesn't replace the People Hub, but by following the Windows Phone style guide, by working on making everything feel like the built-in applications, by ensuring the complexity of the Twitter ecosystem is held back as much as possible in favour of making the interface work as expected, Rowi makes a strong case to me that it should be the default Twitter client on my Windows Phone. Yes, even over the official Twitter client.
Other clients are available, but for many Rowi is the one they've not only stuck with, but have watched grow and mature to be a fantastic tool for managing Twittter. For them this upgrade is a no brainer.