On my Android phone, when looking at the topic list, the default zoom makes the topic names huge and requires scrolling to the right to see the number of replies and last reply. It is possible to zoom out by double-tapping which makes the entire width fit on the screen and this looks good.
Once into a topic though, the zoom again defaults to huge, and it is impossible to zoom out. The text is so big that it is difficult to read (lots of wrapping).
Finally, the reply functionality is hidden and requires tapping on a message to see the button. Not very convenient or intuitive.
I think these are bugs, not design flaws. When zoomed out it works well and looks good.