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][1], 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.)

  [1]: https://anime.stackexchange.com/questions/27527/who-is-this-ghost-from-episode-8-of-shingeki-kyojin-chuugakkou