I think those Magic Genie Bobbin Washers really are magic - but so far, only in the vertical bobbin machines.
They don't work in the 66, 201, 301, 401, 403, 500 or 503 - all of those are horizontal bobbins and there is just enough "height" in the washers to push the bobbin up and allow the thread to sweep around and get hung up on the bobbin with every pass.
They virtually eliminate the tiny little wads of thread on the backs of quilts, though. I won't use a vertical bobbbin machine without one.
If you have big loops on the underside, it means that your tensions are out of balance - there is not enough tension on your needle thread compared to the bobbin thread. Try adding tension to the needle thread about ten degrees at a time until you're getting a nice even stitch on both sides of the quilt. :)