As someone who read the manga while it was still ongoing I enjoyed this a lot as it contains every important scene (except one sweet scene between one of the couples in one's room > read it to get what Im talking about đ) which is kinda disappointing but overall I'm very satisfied with how it turned out. Also the movie doesnt really portray the character development because the movie didnt go too deep into them or rather didnt have time for that. But that's not missing in the manga, actually all four MCs got their fair share of development so thats another reason why you should read the manga beforehand to just fully focus on and find pleasure in the major scenes in this movie.
So my recommendation is read the manga first, if you enjoy it then you will love this movie because you will see all the important and favorite scenes in motion and sound (and with incredible art, just look at those backgrounds, OMG) which is more than enough I would say, something that people who likes Ao Haru Ride (another story by the same mangaka) didn't get in its adaptation.
