Performance and size of NPOT texture in POT atlas?

Hi. I'm starting developing my 5th Android game and this time I'm trying to make it as fast and small as possible.

NPOT textures cannot be compressed but we can add textures to atlases which are always POT. On build time, Unity saves those atlases instead of the original textures.

Now, since atlases are always POT, are they always compressed? And if Unity saves atlases - which are POT - and uses them (loading, compressing etc), do we get the same performance and size optimization as using a POT texture? In other words, is there a difference in size and performance of (i) using POT textures and (ii) using NPOT textures but adding them to POT atlas)?