Hey m8.

It worth obtaining the raid eidolon for sure, and here is why and what you should know:
1) During the off event-raid period(Weekly event that does not utilizing bp, no raid-feature), you have zero use of bp afterall rather than hitting raid. The drop rate is not very good, but if you focus a week on one same raid type, you should have enough to full lb them.
2) The cost to fully LB a raid is 500+1000+2000+4000=7500. After you played for a while,... it is cheap af
3) Only LB raid event ediolon if you do not have a substitute SSR one from event. If you dont, then raid eidolon=best eidolon, obtainable, lbable
4) A 20%atk/20%hp is a good bonus at full LB, the biggest downside is their active use has no extra effect
5) Dont level them up past lv 40 ok...