The game requires at least one 5* shield to beat the mission mode, but because of the stark requirement for radiants, most of my own shields never see past level 4 because "what's in it for me? miniscule shield defense?"
Heck even shield defense UV's are a joke.
So at what point do stop heating shields?
Is there really a difference between level 10 and level 4 ( which is the first level to demand 42 Rads)
I don't heat my 5* shield. I would rather save up those rare radiants for weapons instead.