I used babyplus religiously during my pregnancy and my baby, although premature, has the best nature I can possibly ask for. She hardly ever cries (except for feeding and change of diapers) and seemed to be content whenever she is awake. She can wake and play with herself for an hour without waking me up. Of course, there really is no way to know whether it is because of babyplus, but I will definitely use it again for my next pregnancy.
One thing I still do though, I would switch on babyplus whenever my baby gets fussy and it does wonders. She would stop and go back to sleep, maybe it is a comforting sound for her. Not sure....