I LOVE my rulers! They're a lot of fun to use and make some great designs.
The rulers should match the foot. High shank feet use high shank rulers. Low shank feet use low shank rulers.
You don't necessarily need to lower your feed dogs. I like to leave them up. It gives me a rhythm to work with. Just reduce the presser foot tension, which is the knob on top, above the presser foot.
The woman who invented the Westalee ruler foot and rulers used a vintage Singer in her first videos. Here name is Leonie West. I tried to find her first videos, and they're gone from YouTube. She uses a newer, computerized machine now.