I have had the pleasure of driving both versions of the Plus 8 and both auto and manual boxes are great. However from a standing start, the power delivery in the manual box is instantaneous - there is no lag that you get with the auto box. This is perhaps why the car can be a bit twitchy.
Dixon-Smith always reckoned that the auto version of the Aero 8 was quicker than the original manual box. Personally I thought the auto box improved the driving experience of the Aeromax, but the Plus 8 is a much different car despite having similar tubs. Enjoy the Plus 8 whether it's manual or auto!