They say this will work but considering that some species of crickets can chirp hundreds of times per minute you would have to record them then slow it down in order to count, faster to look at a therometer

Test the theroy yourself and and you may be surprised at what you get.
Count the number of times a cricket chirps in 15 seconds then
add 40 to this number.
What you get should be (or close too) air temperature in degrees Fahrenheit.