What you see below is the very first video I shot underwater, while snorkeling, with a pair or Kodak SP360 4k cameras in their underwater housing. As you can see, parallax issues are minimized, but you still have a seam line that you have to contend with. I learned that its much easier to be aware of the seam line while filming than it is to mask and edit around it after.
ps. sorry for no play controls on the video, but the plugin doesn’t offer them! Still, its in 360°, and you can drag the video to look around.