You can collect photos to use in live shows of the members of both STARISH and QUARTET NIGHT, which is really awesome BUT I wish HEAVENS were featured as well. Heaven's Gate was my favourite utapri song XD
Gacha rates are very low but sometimes you can receive tickets that give you SR and UR cards which is a lifesaver. It's also quite gruelling to get exp points and other items, making levelling up and developing your cards a bit tough if you are an f2p player.
However, I'm disappointed by the story. You have to amass tickets from levelling up to unlock tickets but to complete an entire chapter, you need 9 of them. This means progressing the story is extremely cumbersome and long winded...and to unlock songs, its necessary to have at least 3 tickets...
CONCLUSION: great music, beautiful idols, pretty time consuming game