well, he already got another superstrong one. As they are rare, they could give him enough money to get top grade equipment.
myself, I would first ask around how many servants one can have at once. being such a strong thing it would be a good aid, but unless you have a collector/hoarder mindset or is thinking long goal about different strategies (which is kinda hard because it seems gacha-y) having more of them than you can use at once is kind of a waste.
But as we already know from the cover he can have at least two, yeah pretty sure he is more resisting being greedy than actually thinking things through.
Also, wonder if now that he knows that her real form is actually adult-sized he will stop
hoarding the exp protecting her so much