I like the idea of getting a sudden power-up mid battle. It always disappointed me that pokemon could evolve during a battle in the anime but not the games... Of course since the form is temporary I wouldn't call it "evolution." It certainly supports using your starters more often along with myriad of other Pokemon!
P.S. Love your reaction. The last pic I was on was a mega "evolution" hate pic. Everyone has their own opinions, but complaining about them isn't going to get rid of them. I don't think there are enough people that hate the idea to do that.
Golden Moon already said it but I'll clarify that its Forms similar to the apex of the Pokemon's Darwinian Evolution. As Pokemon evolution is more like Metamorphosis. Or rather it seems to be that way. Amusing btw.
Yeah! These are, without a doubt, out-of-this-world GRAND. However, if I may clarify, these are NOT evolutions, these are their "Awakened" forms. They reach this form when they power up to the max. And when they tire out, they return to their normal forms. For further explanation, look up Mwetwo: The Prologue to Awakening (still in Japanese)