Wow! There's nothing worse than a $650 electronic device so slippery its ready to slip out of your hands an fall to ground any minute. Why the hell would they design it like that? That's what is nice about the n5 in that respect, it's plenty grippy.
It's not just this phone, it seems to be a trend. The M8 is plenty slippery, even the iPhone 6 is tough to hang on to. I'm not a case person either so I learn to deal with it, but I never feel fully comfortable.
I find my iPhone 6 plus is way more slippery than the nexus 6. I have to use it in a case. I find the back of the nexus actually provides a pretty good grip.
We should not need to buy stuff to correct their design deficiencies. My immediate reaction would be to return it! I have a dozen days left to make a final decision.