I think the Swirl Free is formulated like Megs #81 V #7 differences to be more suitable for modern paints. #9 was formulated for single stage paints etc, like # 7, where as #81 and 82 work better on newer paints.
#9 works better with the Rotary, some say to remove swirls it needs it. Swirl free works well by PC.
The #9 is said to have more fillers, other differences are the ranges.
Swirl free from the Bodyshop Pro Range
Swirl remover from the Mirror Glaze Line