I use render cows with few problems. To enable Hypervue, you don't need ultra, go with user settings and edit your rendering settings. You'll need to choose "render to screen" if you are rendering a still, and hybrid motion blur/DOF isn't compatible ( for stills only). Other than that, you should be able to use your cows ok, apart from the odd lighting problem that I've had a few times at random: th light is computed differently from one tile to the other, and E-on hasn't been able to answer clearly on this. Will try rendering again with the new patch.