The Razer Nabu main function is step tracking, which it does accurately, compared to the build-in gyroscope of iPhone 6S and Samsung S6 the differences were negligible. The device can support a lot of abuse and is quite solid, you don't have to worry about bumping it, the rubber protection does it job well. I asked a colleague to test a second Nabu with his Samsung 6S and we came back with almost all positive news, he found the Nabu to be solid design, easy to read screen for messages and ok battery life. He did have some remarks regarding usability of the button when trying to skip music on Android, which required extra setup steps and was a bit cumbersome to use. 

My experience with the Nabu's notification screen was mostly positive, even in direct sunlight the text appears clearly. When you receive several messages in sequence without dismissing them from the band, the orderi in which they are shown on the Nabu is reverse of that on the phone, which can be confusing at times when notifications are coming in from chat applications. 

Playing around with the device the first week we both found the battery to last up to 5 days max, after reducing brightness and toning down vibration to medium/low I could squeeze out 7 days, while this didn't help for my counterpart who received a lot of chat/facebook/whatsapp messages during the day, battery life remained max 5 days for him.

When you reach 15% battery life you'll get a notification to connect the Nabu to its charge cable

When pressing the small button on the side of the Nabu you can dismiss notifications as well as cycle through the different information screens. You can also add camera/music control options to the cycle which will either trigger the shutter button on the camera, or skip the current playing song (or pause/play, depending on how you configure this). While the idea behind these extra controls is great, the execution with only one physical button the Nabu makes it a cumbersome experience. Before you skip to the next song, you first have to cycle through the screens, most of the time taking your phone out of your pocket will be quicker. On iOS music controls worked with any currently playing media, on Android you have the specifically select in advance what music playing app you want to control. Overall the extra information screens are a nice to have, but hardly essential. The screen is mostly used for checking to see what time it is (quick flick of the wrist) and reading any incoming notifications, the Nabu excels in that area.

Another feature of the Nabu is sleep tracking, when you don't move for more than 10 minutes in the evening/night sleep tracking mode is enabled. Every movement is recorded and synced to the application, in the morning you get an overview of much time you spend sleeping/awake. My colleague sleep tracking went quite well, I did notice a lot of flukes with this functionality, sometimes the Nabu stated that I slept less than 3 hours, while I was actually in bed from 22:00-06:00. Was it due to my wife moving around at night? Me being a restless sleeper(?), remains to be seen, tracking with iPhone 5 and 6S in the bed was more accurate for me; the Nabu showed me some weird data on some days

Sleep tracking not always working perfectly for me with the Nabu.

Lastly we come to the Social features of the Nabu smartband, the Social Settings page in the app allow you to link your Facebook and Twitter account with your Razer Nabu, when you do this, you authorize the app to add contacts on these social platforms when you shake hands (or just wiggle your hands) with another Razer Nabu owner. This Handshake feature works exactly as mentioned, no issues with iOS<>Android cross platform here; Twitter send my colleague a message that I started following him (and he following me). 

Another Social feature is the "Pulse" option which will notify you when another Razer Nabu owner is in Bluetooth range. The Pulse is done through notification center which in turn lights up the Nabu display and activates the vibration mode. We found this feature to be mostly useless, and even disturbing. Sure when just passing by this Pulse will only be sent once, but when you remain in the vicinity you will get flooded with Pulses, every few seconds. So that option needs some tweaking from Razer to become useful!

Real Life Handshake translates to me following my colleague on Twitter (and vice-versa).

Keeping Pulse option disabled as the added value is quite low