Keep 2 Fragment of 2030 or limit break?

Do you like using it? Leave it separate until you can MLB it. Two of those at once generate a whole lot of stars

It's probably best to keep 2 since I believe the effects do stack

Keep them until you have 6 then MLB it using 5.

The effects stack. 16 stars with 2 in frontline servants. If you get a third, you will have 24 stars.

MLB (combining the 5) will just give you the effect of 10 stars. Only do this after getting 7 2030s (MLB with 5, put in the frontline, and same for the other 2, total of 26 stars). Otherwise, is a waste of rare CEs.

Effect CE>>>>>>levels of CE