My husband had an about 9 inch long by 1 and1/2 inch wide clear ruler cut out of extra thick acrylic. I use it for FMQ straight lines on my Bernina 440. I have to think about how to place it due to the position of my foot but it helps me. I wanted to outline straight stitch my star blocks in a quilt but use a stipple in the background. I can't FMQ straight lines without my ruler. The reason I had it made fairly narrow was so I could keep it where I wanted it by putting part of my left hand on the quilt and part of my left hand on the ruler. I wear Machingers gloves to help move the quilt and hold the ruler.
Is it ideal? No, ideal would be having a Long arm machine and long arm rulers.