each iteration you do after achive eustrin final a variable (called final eustrin, huge imagination) is increase by one, there are some events already coded in the game to trigger to precise vaule of that variable. for example with a final estruin 1+ you can free relondo harem (simon impregnate them), at 2+ there is a new scene with galvia. there is a very hard optional battle gated beyond 1+, but actualy disabled, poking in the code it's a set of three battles against very strong enemies (physical, arcane and sex type, eustrin is the physical one), but the other 2 aren't in game yet, only the enemy in the enemy list.
we have a limited iteration left, so later you achive it, less content you have. for sake of precision having achieve eustrin final increase your mana in nyst event as well. (neranda will join only after the final state) not needed for anything for now (we need to see the LoB and Fuzkao interaction in the future), but still.
5.2M return is a good return, but if you achieve it sacrificing a lot down the road {something you can achieve without reducing that return}, you cannot think it as a good save. and the fact he cannot fire estruin final content let me think his save is very weak in other section.