The iPhone SE is Apples attempt to go back to the smaller package they are known for. On the outside, the iPhone SE looks almost identical to the iPhone 5S. However, it has much more in common with the iPhone 6S. They share a common CPU, RAM and rear camera. They both run iOS 9 and both have always on Siri.
The iPhone SE can be purchased outright for around $400. It should take you back to a time of small phones.