When I compare the P0 to the L10 moonlight, the P0 is quite a lot brighter overall. The spill on the P0 is much brighter than the spill on the L10, but the P0 is all spill. The L10's hot-spot is a lot brighter than P0's spill.
Note that the P0 has a much wider spill than the L10's spill. So it's a bit difficult to do a direct comparison, but I tried to arrange them so the spill was about the same diameter (which means holding the P0 closer to the wall).
They really serve two different purposes. If you want a very dim moonlight mode that can pick out things with its hotspot, then the L10 wins. If you want a dim general illumination to faintly see a wide area (or look at something up close), then the P0 wins.
Personally, I prefer the P0 as a keychain light, not just because it's a lot smaller, but because I'm usually looking at things up close when I'm using a keychain light. I prefer the L10 as a middle-of-the-night light, because it provides enough light in the hotspot to see things, but no extra light anywhere else.