Really fun technique, although I’m not any good at it! ;D (edit: not my video, just one I saw and tried)
The Noodlers Ahab flex nib or Konrad flex nib work great and they’re more economical than the Wahl or Omas pens. If you like fountain pens and ink you’ll probably enjoy trying this!
I found a picture of what it looks like dry and some info on their blog/site here: Writing on Water