Specs:

The Mi Band 4 and Mi Band 5 are both excellent fitness watches from Xiaomi. Side by side, the Mi Band 5 and the Mi Band 4 look very similar. The biggest physical difference is that the Mi Band 5 is slightly bigger but weighs almost half of what the Mi Band 4 weighs. Also noticeable is the difference in brightness between the 2. In direct sunlight, the Mi Band 5 is brighter than the Mi Band 4. 

The main differences between the two include the fitness workout modes, stress monitoring and more. On the Mi Band 4, there are only 6 while on the Mi Band 5, there are 11. The Mi band 5 has a stress monitor that will alert you when your stress levels are high while the Mi Band 4 does not have this feature. The Mi Band 5 also has a breathing app that will give your breathing exercises  to help calm your body and mind. The heart rate monitor on the Mi Band 5 will also alert you if there is a spike in your heart rate.

Another interesting feature on the Mi Band 5 is the ability to control the camera on your phone. For example, say you want to take a photo but do not have a timer or find the timer inconvenient. With the Mi Band 5, you can place your phone anywhere you like, pose in front of  the camera and take the photo with the Mi Band 5. This feature works on both Android and IOS.

The Mi Band 4 has a slightly longer battery life compared to the Mi Band 5. But, battery life on either device will vary user to user because one user may use the fitness functions several times a day while another user does not. Charging the watch is much easier on the Mi Band 5 than on the Mi Band 4. The Mi Band 4 requires users to take the device out of the band, while the Mi Band 5 has a magnetic charger that attaches to the back of the device.