It reduces absorption time of your whey by 30%. I use a little bit of it w/ my night shake, and that's the only time i'll use soy. Too much soy i think will lower test levels and may increase estrogen levels but don't quote me on that. I just use a little of it w/ my night shake to be safe.
May be not as great as whey but I have never seen in serious studies (on male BBers with enough people, in double blind against placebo studies) that show it is not "efficient"
Best read the last months article on Muscular development. Studies do show that it may not be as effective as whey or egg BUT it can occupy estrogen receptors and act as a natural ani-estrogen in the male body, kinda like Nolvadex. Not to mention it's ability for reducing risk of cancer and a host of other health benefits.
Overall it's a good supplement to take everyday with your whey.