The short version: Watch the TV Series first before watching the movies, then watch the movies just for the experience. The 2nd movie is much better than the first one, but my opinion about the TV series being better still stands. Girls Band Cry Movie Part 1: Youth Rhapsody is a movie where you kinda already need to know the story and watched the original series to be able to love it, it went exactly as I expected, a compilation movie. They had to cut stuff and re-order scenes around to fit in the runtime, and that is exactly why I don't feel like the movie "connect"to me as much, many part of the story were left out for the sake of time, pretty much only Nina and Momoka got the complete story, all other character's lore were either trimmed or cut completely. some small but significant part of the story were also changed, not sure if for the sake of time or not but I don't really feel like it works as well as the original line. I guess the new opening and ending is nice, but that's everything it has going for it. When you try to cut out too much stuff you kinda make the character feels bland, for example, Nina in this case seems like just a unresonable child with no development, and other characters are even worse in that point. So yeah, a "fine" compilation movie, watch the series, then go watch this movie just for the experience.

Now on to the 2nd movie, this one is quite alot better as it picks up just after the the "名もなき何もかも" performance, the latter half of the series is just better in general, lore dump, payoff, character development, you know stuff you'd expect. I'd say the 2nd movie counts as an alternative version to the TV series, rather than the first movie being.... unfortunately, worse than the TV series. Some scenes were cut still yes, but it fits the original story well enough, also the live performance are nice when you watch it in a theatre with crowd. As a fan of the series, its worth it to go just to watch the "運命の華" performance at the end, which is a totally new edit different from the one in the TV series. so yeah, much better than the first.

Overall, I'd recommend the 2nd movie as an alternative version if you don't want to watch EP.8-12 (don't know why though), but the first movie is not a must watch and I'd recommend you watch the TV series instead.

Part 1: 6.5/10
Part 2: 8.5/10
Overall: 7.5/10 (in contrast to 9/10 for the TV series)