Definitely more memory efficient, and much faster to render, I could never populate all those trees on my pc. I've done a few renders with fake trees before, it really depends on lighting, you need them at a distance and backlit for best effect from a low sun, so you can't make out the details.
Search here for 'Forestry Commission' and 'Fake Stone Forest' for more of them in better lighting.
I used Pano2VR, which makes the entire thing for you from your cubic renders.