Absolutely love these rings. INT+3 is amazing at LV10, and still amazing until LV54, when you can get a ring that has the same stats on it for 10k. That's the earliest I'd consider wearing anything else on BLM. HQ LV54 rings are +4 INT but have a 140k price tag on my server, so unless you have a lot of extra gil to waste, these can last until LV72 easy.
I recently decided to try the diffrence between the eremith rings and the +1s at lvl 10 blm i found it did around 10-20 more damage with the +1 version which i thought was GREAT then i got to around 30ish blm and these things become amazing i was in a party with another blm same set up but i had +1 rings and about 3 more int and my spells all hit 30-50 more then the other black mage we swap some armor around and he started hitting spells 30-50 harder then me we then swaped back and yep you guessed it i started hitting 30-50 more on spell so if you ask me well worth the money all you blms rdm and sch if ur gona nuke buy these rings
Now with BLM leveling up to 75 in Qufim these rings have become even more useful. At 72 I was using the +4 INT rings an relized I was only getting +1 when level synced to 18~23. With these on you get the full +3 INT and your nukes will be more damaging and get resisted less. Was still wearing these when I dinged 75 in qufim recently.