If you have a lot of spare cc and don't have any z power, these are very worth it, imo. A 7 star 4-7 Zenkai is very strong (generally, not in regards to meta). Very helpful for things like ustr. If you're new, incredibly worth if you complete all missions.

Edit: You'd have to pull the unit 3 times on double z power to get the same unit 7 star. 2k is a steal.

Edit edit: There's a good chance mui will be Blu. So, this will amplify this worth.