In spite of being an older device, Xiaomi Mi4i is the winner in the battle of these two mid range phones. It has a much sharper display, the camera is better too. The downside to Xiaomi is that one cannot expand the storage. On the other hand if you are looking for fingerprint scanner in your phone, then go for Lenovo K4 Note.
Design And Display
While both the phones are made of polycarbonate body, the body of Xiaomi Mi4i is unibody and hence its back-plate is non removable. On the other hand, the back plate of the Lenovo K4 Note is easily removable. I cannot remove the battery on the K4 though. The overall build quality is decent enough on both the devices.
Both the phones perform well when it comes to multi-tasking but Lenovo K4 Note is a step ahead of the Xiaomi Mi4i because it does not heat up much and has 3 GB of RAM. Do note that these phones are not meant for heavy gaming.
The camera specs are same however, the image quality from Xiaomi Mi4i is much better. This applies to both the front and rear cameras.
Both the phone provide atleast one day of battery backup which is decent.
Lenovo K4 Note comes with theatre-max technology which is something new. The phone when put in a VR headset creates a virtual theatre in front of your eyes. K4 Note also comes with a fingerprint scanner.