I flew one in a Consolidated 1/2A Half Fast and it didn't overwhelm the model. Just slightly more than a Baby Bee it still ran best with a 6/3.
So it wasn't the most powerful .09 about equal to the older McCoy Sportsman series.
It ran best with a 6/3 or 4 and was economical on fuel. If run rich and it burped it could run backwards.
I saw a lot of really mishandled motors but I never saw a Fox 09 have problems with the ball socket. It had a harder alloy then the Cox motors. They were an interesting motor but didn't sell very well as it really didn't over perform some of the better 1/2A examples. Believe it was 1958 to about 1961/2 part of Dukes 'Rocket series.

It did well on a Goldberg Stuntman 23 a few years ago.
Dennis