I'm running every other person, place and thing in the campaign - handling a high level mage's Simulacrum isn't going to be a problem. Heck, I'd wager that it will actually make my life easier, as I can use it both as a plot device and reduce the chance of player-driven shenanigans.
[sblock]I mean, the Simulacrum is, ''..friendly to you and creatures you designate. It obeys your spoken commands, moving and acting in accordance with your wishes and acting on your turn in combat.''. When DMing, I'd take that as it'll have to do what the character commands it to do, but it's still a free willed creature, one that, while friendly at first, could rapidly become disgruntled if it considers its treatment unbecoming. Might not be able to do much about it of course (I COMMAND YOU TO NEVER BETRAY ME!!) but it's a lovely setup for potential betrayal. Of course, this is assuming the creator was being unkind/cruel - a kind/benevolent creator could enjoy quality time with their newly created best buddy.
This does raise the question of the Simulacrum's personality. Is it the same as the creator? Not so good news for less pleasant/evil/cruel creators. Sure it's loyal on command and friendly when created, but does it remain this way indefinitely, regardless of circumstance? How much agency can a Simulacrum exercise when not specifically being commanded? I'd assume all of this is in the hands of the DM-Player chat before the spell is cast (heck, when the spell is even considered.)
Hmm. Anyway, if I was given total control of my character's Simulacrum, I reckon I'd play a lovely creator wizard person, best buds with his creation - tea, biscuits, dynamic adventuring duo. There'd be tears if it/when it dies. But I'd also be sure to discuss matters of agency/free will and factors that may/may not affect its relationship between creator and Simulacrum. Juuuuust to be sure. [/sblock]