Ok, it's actually called Emergency Battery Saver Mode and it's not the actual Ultra Battery Saver Mode that is currently available to China ROM users.
Overall I would say its' very effective especially when it comes to conserving battery over night without having to switch off your phone entirely. I just have one issue with it.
For some reason when you turn off the feature, notifications don't stream in as usual. You'd have to manually open your social media, email apps etc to get notifications even after a reboot.
It also turns off accessibility for all your activated apps. For some reason when I shot the video below, it didn't do this though. It acted normal. Anyway, the guide is in the video below. It's pretty simple to follow.
Install Activity Launcher, run the app, scroll down to Battery and Performance, click and hold the second Extreme Battery Saver option that ends in ExtremePowerEntryActivity then create shortcut. Click on the shortcut on your desktop and enable Emergency Battery Saver Mode.
That's all. Enjoy!