Is it safe for me to watch Shingeki! Kyojin Chuugakkou as an anime-only viewer?
I recommend watching the anime first as a good overview of the series. Then read the manga, to cover any: plot holes/extras/gags and to get more info. It doesn't really matter because the anime (most of the time) follows the manga (In Soul Eater, the anime and manga are different but the story continues differently so it isn't spoiling anything because it's a different story).