I think that question that the OP was trying to raise implies that certain items, like Life Orb and Leftovers, are obvious when used. However, for other pokemon like Scizor and TTar, who are viable Choice Band users, and Garchomp, a viable Choice Scarf User, would the presence of Two Mega Stones on a team provide more benefit/flexibility than say the above mentioned choice items?Frankly i find this idea pointless. If a pokemon is viable both with and without the mega stone it already create mindgames naturally and if it inst viable without the mega stone then youre just using shooting yourself in the foot. It just doesnt make any sense to me.
Personally, I have no problem with it. In the end, as long as the builder of the team is happy with the final product they are presenting, whether on PS or on Wifi, then having to mons that can utilize their stones given the appropriate situation is nothing to sneer at.