A guy I know uses one on his land for pheasants in SD. He says he believes it works as far as being able to release chicks with pretty much the same mortality rate as a 5-week-old chick hatched in the wild. My understanding is that he releases hens in the "down" years in order to try to bolster reproduction the following spring. His thoughts are that there are always enough roosters to get the breeding accomplished. Hens are the issue.
I can't recall the source (possibly Pheasants Forever article?), nor am I going to research it. But a few years ago I read an article about hen/rooster ratios. Basically, you need 10% of the rooster population to survive to breeding season to repopulate the pheasant population back to what it was the previous fall. And in fact, you really didn't want much more than 10% of the rooster population to survive fall hunting season and winter each year. When conditions get tough, the roosters drove the hens out of prime winter cover and food sources, lowering the hen population and therefore the overall pheasant population.