I have made my own ruler from another square ruler. I wanted squares in a size that the Twister doesn't come in. I used clear tape on the top of my ruler and marked the lines on the tape with a sharpie. I made sure to put the clear tape on the top of the ruler so that when I peeled off the tape the ruler would be okay. If you put tape on the underside where the lines are, I think peeling off the tape may take off the ruler lines.
The benefit of the actual Twister ruler is, it has little rubber feet underneath so the ruler is stable over the seam allowance bumps and doesn't slip. If the Twister ruler is in the size you want, it is worth it.