Is it safe for me to watch Shingeki! Kyojin Chuugakkou as an anime-only viewer? I have only watched (season one of) the Shingeki no Kyojin anime, and have not read any of the manga. 

As I watch the Shingeki! Kyojin Chuugakkou anime, which is airing this season, I am starting to get a sense that I am at risk of being spoiled for content which is currently manga-only. Nothing glaring comes to mind yet (though that could just be because e.g. I'm failing to notice gags that are based on manga-only content), though there's a character from episode 8 who I don't think I know, and an altercation between two characters in episode 3 that I was told comes from a flashback that hasn't been animated yet. 

Can someone who has read the (main) manga and is watching Shingeki! Kyojin Chuugakkou (and perhaps has read the source manga for that) tell me how much of a risk I'm at of spoiling myself for content that hasn't been animated yet? 

(If there's a high risk of spoilage, I figure I may as well put it off until season 2 airs in 2016.)
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).