When FMQing I can do most things freehand but I have trouble FMQing straight lines. The last twin size quilt I did had Sawtooth Stars. I wanted to stipple in the stars but SITD around the stars. I added washers to a regular FMQ foot so I could use one hand on a 1/4 inch thick ruler beside the line I wanted to quilt and pull the quilt along the ruler. I put my machinger gloves on and keep my left hand on the ruler/quilt and my right hand on the quilt. I did not have any trouble moving my quilt and ruler at the same time as I stop to re-position as needed.
As you can see from the pictures of the Westalee foot, it works better then my homemade foot PLUS there are neat rulers to use with it. Yes, it does take some practice but if you buy the foot and some of the rulers, you can quilt on your domestic machine and do not have to mark lines. I am intrigued!