Used the planet buster a couple times myself. I don't fear any of my allies nor enemies besides the groxx which I can still easily beat but takes way too much time to destroy all their planets.

I did notice some allies becoming unhappy when I used the planet buster for the first time, not sure about the other times though.

Maybe I'm just lucky as I find the entire game extremely easy so far. I currently play on normal and wish I started of with Hard. The only thing I find annoying is them attacking me every time as I can easily beat them but find going back extremely annoying.

Also I play as warrior and I crush any species that attack me.
As a wise man once said. "Peace through POWER !"

__________________