John, I've never used one. Fortunately I have been able to make a couple of visits myself and had a couple of friends do so as well. I would not hold out a great deal of hope as far as the 55th FG is concerned, as their data seems to be sketchy at best. Unfortunately several fighter groups had much of their records destroyed when returning to the US post war. Included in these are the 339th and 357th where I have never found much of real interest to me (squadron line-ups, aircraft used etc). However, there are many independent researchers that you could get quotes from and the NARA page for those specialising in military matters is at:
https://www.archives.gov/research/hi...topic=military
Best wishes
Peter