I'm going to give you my very unscientific response, please note this is only the opinion of another old fart. I did all of the homework, and read all I could find on the subject. I noted that it is reflective, in my little mind this means that, since it is white and has shiny things in it, it reflects light, mainly sunlight. I had no illusions, or hope that if I painted it on the inside of anything that there would be any measurable or perceived difference. That's not what it was designed for. I considered buying just the beads and mixing them with some locally available paint.
In the end I finally decided to go the whole route using all of their products.This meant two kinds of primer, since part was old paint and part was new aluminum. I don't remember the cost, but all came to somewhere north of $700 including shipping. If I weren't so lazy, I could look it up. I did the prep the way they suggested. I bought an airless sprayer from HF. The primers are a bitch since they are clear and, just slightly thicker than water. I used the clear coat and it was about the same consistency as the primer. The sprayer worked well but, I think if I had it to do over I would roll everything on. It was a bit hard to control thickness. I did my painting in what was the hottest summer we've had in Indiana in years.It didn't work well with masking tape, I found it best to cut along the tape. I ended up putting reflective tape at the color change to cover up the rough line.
Note I didn't take any temperature readings, the daytime temps were hovering around 100, the sun was shining, it was hot. Now for the really scientific part. My bus came from NM with the standard yellow roof. When I was doing the final clean I was walking on the roof with just my socks on, it was almost too hot for my tender feet to stand on. After the coating, when I was putting marker lights back on, I was able to rest my forearms directly on the surface. It was warm, but not remotely hot. Try that on a yellow roof. Inside the bus with the windows closed, I did take a temp reading on the ceiling, it was about the same as outside temp, and still felt hot. With the windows open, if there is any air movement at all it feels about sitting in the shade of a nice tree.
I run at times, 4 computers in my bus, along with a laser printer and a commercial dye sub printer and don't have the luxury of air conditioning. I run extra fans on everything and don't usually have an overheating problem.
Note, all of the white is reflective beaded paint. The surface is rough and feels slightly rubbery to the touch, which makes it a bit hard to clean but, I'm not really known for doing all that much cleaning to the outside of my vehicles.
Do I think it was worth the money spent? yes
Do I think just painting it white would do the same thing? maybe