I'm curious to see some replies to this. Urine diversion basins are popular in Indian eco composting toilet circles, but to be honest I've never seen one functioning after a year of use. I've only seen eager descriptions of how they are going to work. However, I do know people who say they use them and they work.
My composting toilet has everything going into it. I use sawdust or dry fallen leaves as the cover material, and according to Joe Jenkins (of
Humanure fame), using a high-carbon cover material and the full mix of urine and feces gives the best carbon-nitrogen ratio and works great. I haven't had much problem with it. I think if you have both males and females using it and provide a stand-up urinal for those who prefer it, it would reduce moisture (if you need that to happen) without much fuss. If all urine is removed, it's hard to keep the
carbon ratio and moisture good enough to decompose feces fully and safely. Though some toilet designs may require it, I guess.