I have the one for the Janome 7700. I've used it a couple of times early on in my quilting "career".
It was a bit pricey (even though I bought it used), and to be honest the finished binding just looked "okay". The way it folds the fabric strip is twice towards the middle from the outside, so you actually only have one layer of fabric going over the edge of the quilt. It basically created seam binding on-the-fly.
For quilts it wasn't worth it to me. If you have projects that use a lot of seam binding and wanted to make your own rather than buying the little packages, it could make sense.
Michelle