We've got one and it says that you should remove it at 6 months, I assume because by then the child can reach it and play with it. DD is 14 months old and she likes to look at it and play with it when we are changing her nappy (we've got one of those over the top of the cot changemats.) I don't have any plans to remove it. Ours is a kidsline one I think, fairly simple and plays music. We rarely use the music one these days.

Another option is one of those Fisher Price things that light up and put things on the roof when it's dark and also plays music??