Mostly, I’d guess, it will appeal to people who currently have a four-inch display phone. Going back to it from the iPhone 6s Plus with its 5.5-inch screen, took some doing - why, the entire dear little iPhone SE fits within the 6s Plus screen. Using the keyboard on the SE was a learning curve after the expansiveness of the 6s Plus.
The front FaceTime camera is still the same sensor as iPhone 5s but benefits from the new ISP and from a Retina Flash. I’m not sure why it didn’t get a bump to an iPhone 6s-level 5 megapixels, because selfies really are a thing and really do need the better camera.