I too was just looking at this product because it is so much cheaper than Celsius and it is marketed as a substitute. I also thought it was strange how different the AI's are but maybe the mode of actions are similar? Who knows, but I did read this on the label for Fahrenheit - "Do not apply to turfgrass under stress due to high temperatures (above 85°F)." To me, that's the whole point of Celcius - no temperature limit so it works spring, summer, fall. No way I could use Fahrenheit from June-Aug, according to the label. Better to find someone to split a Celcius bottle with.
Fahrenheit Label : https://www.solutionsstores.com/amfilerating/file/download/file_id/1361/