Was recently flying CBR-MEL on the 717 and received email offer to buy a Neighbour Free seat. Only problem was that my partner and I were sitting in 4A and 4C (there is no 4B on the 717) and so did not have any neighbours. We were both on the same booking. I didn't go through to buy it, so not sure if they were going to propose to keep 4D (across the aisle) free, or if it was just a glitch. Weird..