When I lived in Nashville, I used them all the time.
I don't like the Economy parking. The buses were slow and there is NO security there so if you arrive late at night you are walking to your car in the dark. (I once had one of the lights on the pole break all over my car. Walked to the phone and called security as a I wanted a report for the damage. Took well over an HOUR for security to finally come. There had been glass all over the parking lot for several days... they never noticed etc.) Flight Park is great, they watch the cars and when my friend's battery died they had her jumped off before she got there from the airport, once again in BNA's parking lots you are on your own! (Not to mention that I got tired of the RUDE employees BNA hires)