yeah... eidolon 25AP quest mob is almost as hard as boss... and then u have to do it 3 times in a row. i don't dare to bring friend anzu with it.
i think it also depend what u need to level more for immediate power boost. but i see trickle of weapon and eidolon xp when farming other stuff actually better for eidolon. each common R eidolon is 60-70xp, or more if same element.I would definitely go for the eidolon enhance material SP quest as those guys are strangely difficult to get while you can get weapon enhance materials from most regular stuff. Of course if you really need to level something, do them. For now, I only ran each once to get the gem rewards.
there not much point to do weapon modfod quest if ur weapons are all not uncapped because lv40 is quite okay just using drop from normal farming. but once u trying to get ur SR weapons to lv70, the SR modfod is love.