I have done a fair amount of ruler quilting, and I think it does make FMQ easier, just because you don't have to worry about where you're going with the quilting. You place the ruler and then sew along its edge. That makes it easier to acquire the basics of coordinating your hands and the foot pedal. That said, the Westalee ruler foot is not the greatest, and their insistence on giving you very thin rulers if you have a low shank machine is misguided, I think. It sounds like your ruler slipped under the foot. The foot might have been set too high, but I also had trouble with the Westalee foot sort of swiveling up in the front.