When I tinted the windows in my bus I was wary of paying good money for something that would turn purple and blister in just a few years' time... we've all seen how awful that looks in the back windows of "some car on the road."
I found my way into a few local window film dealers' shops and was introduced to Solar Gard. Solar heat rejection was my biggest concern and they had some demos with heat lamps that really sold me on it. Unfortunately their installed price was high and they wouldn't sell me film straight off the roll..... so I became a Solar Gard dealer and bought direct instead. I think it was the HP Smoke 35 I used in my first bus, which I've since sold, but I also used it in the front windows of my cars and even in a couple windows in the house. It's been about 4 years now; it still looks good and I still appreciate the difference it makes when sitting with the sun shining through the window.
Solar Gard's web site has a summary table of auto tint laws
and a table of performance results
you may find useful no matter what brand you choose.
In a mobile application "high reflectivity" may have a good chance of getting you into trouble. Consider also that a mobile grocery is commercial, and (I believe) tint laws are more restrictive for commercial vehicles. Looking at the solar heat rejection figures on Solar Gard's site I think you may be able to achieve your heat reduction goals without resorting to high reflectivity.