We used FB for the first time in June and I had also read you couldn't use the garage counter the first time.
After landing we went straight to the garage counter...walked right up to the window, no wait. They served me as if I were a long standing member having many rentals. That's how easy & seamless it was.
Something I have noticed twice while booking with Budget at MCO pickup. The FB price is higher than the non-FB price! So what I do is book the non-FB and call and have FB # added to the reservations. So do the comparison before booking.