It's only a little "similar" to Gate because of the modern vs medieval military, but the rest of the story structure is completely different. I recommend also reading the Summoning Japan web novel, the English is 1/3 fan translated, while I read 2/3 of it with Google Translate (still understandable). The web novel conveys a lot more details. The manga changes a bit of the dialog to fit it in the illustration panel format. A lot of Summoning Japan has to do with politics, policy, and resource/land conflicts. There is also a background arc of mythology, as introduced in this chapter. One of the biggest differences is there are no main characters in this story. I only watched the anime and seen the manga for Gate, so I don't know what the web novel is like. But I like Gate for the comedy, main characters, and heroism. On the other hand, I find Summoning Japan to be really enjoyable for it's grand scale of world building and intense conflicts. It kind of reminds me of the world of Earthsea, where people go on adventurous journeys to discover unknown lands across uncharted seas, but instead now with aircraft carriers, supersonic jets, and space satellites.