So the part I like about Eureka is it's a grind towards something even though I completed my +2 weapon in 1 day total time as while everyone else was ******** "wah wah this is FFXI grind gtfo this game wah ah", me and FC mates were poppings NMs, leveling, converting anemos crystals to protean and gained over 1300 after 6 hours total of Eureka. Not even 6 hours straight, was over the course of Tuesday and Wednesday. The armor is worthless as I'm in full Savage gear (which is beyond easy but people still won't do it) and the ilvl is still below Tome gear, which by now you should have a near full set if you didn't space pieces out between jobs.
They clearly intended Eureka to be released alongside 4.1 content as the ONLY PURPOSE to the armor is glamour unless you absolutely REFUSED to do content in this game and you're still rocking Verity gear. Having 5 guaranteed slots are nice, but not really incentive enough to downgrade about 20 ilvls.
It is indeed for your relic. The process is:
100 + Job quest weapon
400 Crystals for +1
800 Crystals for +2.
3 Pazuzu Feathers for augmented versions - Which requires being level 20 in Eureka and spawning the actual NM. So no one will see the final stages of "Stage 1" relic for about a few more days at best and that's IF the feathers are 100% drop or random drop like the FFXI gear is.
With all that work, you could go into Byakko Ex and get an ilvl355, or, you can buy your mendacity weapon and get a 360 weapon.
So all in all, despite people saying it's "a FFXI nod" it's more of a nod to the leveling you did in XI, the only fun I've had in Eureka in terms of being reminded of XI was fighting Serket and Fafnir, because you can't just zombie it like 99% of FFXIV content and have to actually deal with mechanics, while you have people who clearly think it's regular XIV content dragging adds to the boss killing everyone.
So at 4.9 or whenever SB ends the relic weapon will be BiS, but for now, this content is a fun little distraction after you complete the game on tuesday every reset. Right now about 30k from 20 so I can finish the relic. You can't get the items ahead of time as you NEED to be level 20 to even obtain the drop or the last 2 spawns of Pazuzu were just RNGesus giving everyone under 20 the finger lol.