I like them. Simple, minimalist, and clean. They actually look nice on screen and work just the same as the old nav buttons. Honestly it would take all but a few minutes for a new user to figure out what they do.
I'm also confused by the idea that a phone requires an actual home icon to denote "home". One of the biggest selling Android devices, the Galaxy S series, has a physical button with no iconography and I don't think people have problems figuring out what it does. In the smartphone age, people are seemingly hardwired now to know the the center button = home thanks to Apple and Samsung. Now I wouldn't mind in the slightest if they reverted back on the change as I like the previous nav buttons all the same.
Just my opinion.