If you have issues with it, here's a tip:
Most Mega Evolutions, even though the Pokemon have been trained to Mega Evolve, the sudden surge of energy will hurt them mentally and physically. They can lose control and be unable to listen to their trainer anymore as they are more focused on trying to fight back the pain. Imagine overflowing a balloon with water until it is close to bursting. That's basically what happens to a Pokemon when it Mega Evolves, with the Mega Evolution energy being the water, and the Pokemon is the balloon.
With Altaria, when it Mega Evolves, it apparently becomes more sociable, less timid, and has a better soprano voice, which a regular Altaria's voice already puts people in a dreamy-like state due to how pretty it sounds. I believe the pain it undergoes through Mega Evolution isn't as much as other Mega Evolutions, but it is still quite hampering on their minds and bodies. They would have to go under extensive training to transform and to stay transformed and to get used to their newfound strengths and weaknesses as a Mega Altaria.
I don't know about the personality your Altaria has, but it could change upon Mega Evolving.
So basically, Mega Pokemon are a little harder to control due to numerous reasons, whether it be the Mega Evolution energy changing their personality or the energy actually hurting them to the point of becoming numb to everything and will fight until they exhaust themselves completely. I believe your Altaria won't go through too much pain. Although, it gets an increase in power and physical defense due to the rampant energy and extra fluff, but the speed, special defense, and stamina don't change. Just as long as you play this as so, then there won't be any problems. XD
If we do see some OPness, we will tell you