Yes - I do have one, and I use it all the time except for when I am sewing zig zag or decorative stitches. It really helps with piecing, sewing and machine embroidery. I have a Pfaff that tells me to remove my straight stitch plate when I chose a stitch that won't work with it and I am forever grateful for that feature otherwise I would have a whole lot of broken needles.
It really is worth the cost of the plate. Go get one.
Julie