Especially for me, going from a massive 5.5 inch iPhone 6 plus to just 4 inches, it's hard. I don't think I could get used to it. Just holding my old iPhone 5 is really weird, and it's extremely hard to type on it because of how many mistakes I make. This iPhone is like a 6s packed into a tiny little case. It has the same 12-megapixel camera, and even the same A9 processor. For me, this isn't enough of a difference to upgrade. The display is 1336 x 640 which would be a downgrade for my 1920 x 1080 iPhone 6 Plus.
To conclude, I don't recommend upgrading to this new phone. If you have an iPhone 6, 6 plus, 6s, or 6s plus, stick to that. I hope this helped, thanks for reading!