Yes, I have used every rainbow shard gacha I could and now I'm at 815 shards. I'm only hesitating to use them because of RRose. Well, and there are so many girls I don't really have a good idea where to start from. I looked at this page and it seems to have some good suggestions, and this thread has been helpful too, but it's difficult to decide without really knowing the meta.
Anyway, I went with Ume for the 6* ticket. Thanks for the suggestion. I was initially leaning towards Anemone, because of her defensive capabilities and super counter, but Ume is a beast and I really need the skill activation, especially with the lack of skill flowers.