Wow, that's wild that you can sometimes see the muscle reverberate. I experience something kind of similar to what you described.
My RLS starts at that location too but feels like it's tightening until the whole muscle is clenched. Then it relaxes and once it's fully relaxed it starts to tighten back up again. This continues and increases in frequency and starts to become painful. That's when the electrical impulses, you also experience, kick in. After a couple more minutes the urge to move my legs starts to increase until it feels like I will go mad if I don't move them.
🥄🦄 Ray (Team member)