While it was not exclusively GJ (swing in general) it did lean towards GJ, and definately my (even very rudimentary) use of GP helped.
Essentially at this point, of all the patterns in the book, I am doing only the downstroke so far, having not spent enough time trying the others yet (that will change soon). I did resort to alt-p some, but my emphasis was on the rest stroke.
What it did for me... I was loud a-plenty, which in the past was a HUGE problem for me... and, today I have zero soreness in my picking arm, which also was a huge problem for me in the past, even to the point of tendonitis.
Comments
out of all guitar styles you could have picked, gypsy jazz would be the one to challenge your arm the most.
initially when starting out at a jam with people never met before, or a gig I would have a problem with my alt-p falling apart BIG time due to nerves.
My arm would become tense due to natural nervousness until warmed up a bit, and therefore i could not control the picking as much as needed.
This seemed to be much less of a problem for me with GP. I concentrated just on relaxing the arm as much as possible, let gravity do the work on those down strokes, and though it still took me awhile to get smooth, it was a vast improvement over alt-p for me.
I don't understand the comment about it being challenging for the picking arm... When done right the muscle tension is minimal which is a big plus for me, your right arm shouldn't feel tired or sore at all, it's all in the wrist and gravity does most of the work for you, if your arm's getting tired you're doing something wrong.