That was very interesting. Thanks for sharing it. The person "Candy," who left a comment on the link you posted, shared what I think, too. Maybe it just means the researchers need to do more and better work in order to prove the obvious to skeptical scholars.
I also expect that people who are selling products might overstate their case sometimes. :Shrug.: I don't think using sign language would improve a hearing child's self esteem or making parents and baby bond better, but other benefits ought to be obvious.
For myself, I don't need research. I just think about these questions:
Is it better for me baby to be able to tell me she's not hungry, she is thirsty, at 6 months, or at one year?
Is it better for my baby to be able to tell me he wants the ball, not the battle, at 8 months old, or at 15 months old?
Do I want to be able to be sure why my baby wants sooner, or later?
The answer to all those questions is the first part of the question- sooner, not later. Obviously, then, I think signing is good for hearing babies.
My daughters could all talk orally very early, before they were one. My son could not talk until after he was two. He did not talk very well at all until he was four. We used a lot of sign with him. I can't imagine how frustrating his life and ours would have been if he hadn't had the communications skills only possible for him with AsL.