Hi, I have used the Wilton spray mist colors. I usually do a quick test spray on a piece of paper towel to be sure it doesn't come out "spotty" but I have not had much trouble using them. I teach cake decorating in Midlothian VA and whenever I teach Course 1, I bring a cake into the first class and decorate it in front of the students. I bring along 2 roses I make at home that I spray color. I use pink on one and violet on the other. They usually come out great!
I also used the spray color red on my carousel cake. The bottom tier is fondant, but the top tier is buttercream. I made a wax paper stencil and sprayed the scalloped shapes on the sides of the cake. I didn't get a perfectly sharp edge, but I think it came out fairly well. Take a look at the 3d Carousel (top tier) in my photos.
I do point the sprayer over the red dot. Don't know if it helps, but I don't get much of a splatter problem. I do spray lightly and if I need it darker, I wait 5 or 10 minutes and apply another light spray.
I use them mostly for background color or for coloring the sides of a cake (I cut a piece of parchment paper the size of the top of the cake to cover it and spray the sides of the cake while turning it on a turntable.) I also used it for "ground cover" on my construction site cake. I used green and a little brown to get dirt and grass colors as a base.