We received this for our daughter. It's one toy that really helps babies go to sleep. She's used it up until just recently, when she moved to a big girl bed.
This toy attaches firmly to the side of the crib. You also have screws covering the batteries (3 C batteries), which makes it a little difficult to switch them out, but at least the children can't get to the batteries. Battery life depends on what mode you set it on. We usually used the full mode, with fish swimming, lights flashing and music playing, and each set of batteries lasted us about three months. You can also set it at music only or lights and music only.
There are five different classical songs and three different soothing noises. You can set it to play just one or to rotate through the songs. However, when you switch the mode, it resets to playing the first song repetitively.
Our daughter really enjoyed this toy. It was very useful in getting her to go to sleep quietly when she was in her crib. I only wish they had something similar for toddler beds!