Going to be honest, I don't really see the appeal of the Mandred guardianship. I admit i enjoy the meme of "c'mon Mandred in and out 10 minute adventure" so i would be all about it when he's 15 or so and old enough to actually take part in adventures rather than just be a dead weight.
But i also just don't see Mathilde/the thread doing that. She generally takes risks that put herself in danger. But almost never allows others to take a similar level of risk. As can be seen in the demon fight during the expedition. She also almost always sticks to the letter and intent of her assignments. Which definately does not include random adventures even to 'secure' places like Larelorn or the underway passage at K8P.
He's also not gonna grow up hating wizards, regardless of what option we pick options. We're his godmother! We have access to him on a regular basis, enough that Mathilde can see and pounce on any such indication should it raise its head. And that discounts any other wizard who have access to him.
The only real argument for it in my mind for this over simply being a free agent is that we could be a better protector than 99.9% of the guards he already has. With LM tier magic and a runefang tier sword. But i've seen no indication that the Prince is in any more danger than a regular emperor to-be would be