Eheim - Ebo Jager heaters ARE fully submersible. the warning has to do with some registration and patent/name issues having to do with where they're manufactured now. not to worry. all mine are UNDER water and have been for a long time.
I have a smaller one that has a water line indicated on it. It says not to submerse past that line. Then the larger one I have on my 90-gallon I took out and it doesn't have that. Weird.