Aggron, basically, became Aggronier. Higher attack, higher defenses. Ok, that works. 230 defense is no laughing matter, and now sporting a nice looking base 140 attack, Aggron just might be hitting harder than ever. But, it loses Rock Head as a mega, so, no head smash spam for you, but filter gives it defensive merit. However without any recovery to speak of as a mega, and having lost Head Smash's usability, Mega Aggron is in my opinion, just a novelty, and more often than not, it would be favorable to run regular Aggron, with the benefit of an item and Head Smash, and leave a spot open for another mega-evolution. RU shall continue to be Aggron's home in my opinion.