I have one that i used for my son during daytime the first 3 months... he needed that extra ''womb'' feeling that even a sling couldn't give him! as soon as he started moving a little bit when we was sleeping I took the thing down... I didn't want to take anychances!
I don't know if I will use if with my daughter. I would be afraid that the little one would see this as a swing and try to push her around...