I have a Janome 6600P. I was all set to purchased the blue bobbin casing. The Janome rep was at the quilt show. He told me to save my money & practice. On the Janome 6500/6600 forum I am on the ladies say the blue casing is just the ticket. Later you notice some say well now they have FMQ down they don't always use it.
I am going to try the additional practice time and hold off buying new parts. I was going to get a different foot also. He said it wasn't needed. For now I will go with the darning foot included and we will see what happens. I will watch this topic to see what others say.