I wouldn't want the fixed mobile wheels facing the same direction you push/pull the work piece. If resin or wood sap makes it difficult to push a work piece you could end up pushing the machine.
It's a big "Your mileage may vary" as far as upgrades at time of purchase.
Try to get 25% off accessories at the time of purchase and see if this will apply towards the Byrd head which is something I would have considered if I didn't purchase my A3-31 from craigslist.