The specials are definitely a great watch for anyone who enjoyed Girls und Panzer.
There's side stories, sequal episodes, and episode additions. Overall the mood of the specials felt a little different from the feel of the show but they just as enjoyable.
EP 1: This is just a recap episode of parts of the first two battles with commentary over them. There's some minor additional information on strategic choices and tank information. Overall this episode doesn't add much and it's the only one I'd recommend just skipping.
EP 2: A standard camping episode with a bonus of everyone deciding to be in swimsuits.
EP 3: The most interesting
episode by far. They go into detail on answering questions you may have about the series and school ships.
EP 4: A full presentation of the Anglerfish Dance that had to be performed after losing the school's first match.
EP 5: An addition to the match against Pravda High that follows Yukari and Riko on their scouting expedition. This one was a lot of fun.
EP 6: And to wrap it all off, a sequal episode where the student council hosts a celebration for winning the championship.