I'll admit I did some rerolling (had to get SSR Ramuda lol) but rates are pretty good and I got an SSR nearly every time.
The game looks great, if a little cheaper than some of the bigger name games, but it has a distinct style and sound, which imo is the most important thing for a new gacha game. Especially since a lot of rhythm games have 2020 release dates.
Not sure how good the story is since I don't read Japanese but the cutscenes I saw were well made and dynamic despite using still sprites rather than live2d, which has become the norm lately.
Overall, ARB looks and feels super fun to play. There's a lot of room for improvement, and I have high hopes.