Viper works okay on light duty degreasing and just use a pump sprayer to rinse.
On the real thick nasty greasy coils, I'll brush off what I can and then I'll wet the coil down with some warm water and then use straight Nu-brite out of a spray bottle. I know straight nu-brite is frowned upon, but it really works off you're careful about what you're doing and rinse thoroughly.
I'm not a big fan of the KO blaster. It works okay, but it takes a lot to use effectively and cover the surface area needed.
Some of the kitchens I work in use a orange colored degreaser made by ecolab. It comes in a squirt bottle and the stuff really works!!! Way better degreaser than KO or viper.