I toy with the Twitterrific and Twitter apps out of curiosity, and I use Tweetbot because it just works.
Although it’s an older design feature it’s still one of the greatest: the two-finger swipe up and down to recolor the app for light and dark mode. During the day I use the light mode, and by night it Tweetbot goes stylishly dark. It makes it easier o the eyes and puts a smile on my face.
What I noticed about the redesign is the additional white space. It’s subtle but it’s there. Padding and margin between the content, buttons, and menus is a little more pronounce, freeing.
This is one of the first third party developer apps on my phone that’s updated UI design with iOS 9 in mind. Corners are rounded and symbols are resized. They’re great touches that respect Apple’s style.