Personally I wouldn't pay money for this add on. Well I might pay 5.00 Euros. Its probably a Spit MkI skin with John Dundas's markings on it and the same for Helmut Wick's 109. It will probably be a single mission that sets them up for their (alleged) dogfight near the Isle of Wight. You can do that yourself in the FMB.
http://en.wikipedia.org/wiki/Helmut_Wick
You may also like to know that a few moments after John Dundas shot Helmut Wick down he was allegedly shot down and killed himself by Wick's wingman Rudi Pflanz.
http://www.luftwaffe.cz/pflanz.html
I say allegedly because it is widely believed it was JD that shot down HW and was then shot down by RP although there is only fairly compelling circumstantial evidence (matching of records, known positions etc).
It will probably install (copy) itself to your missions folder.