Hi Ellie!
I recently purchased the Gym Style workouts and love them!
Pure Strength workouts are fantastic and I use them regularly, but Cathe really kicks it up a notch with the Gym Style Series.
In the Pure Strength Series, Cathe does more traditional moves and uses lighter weights than in Gym Style.
The Gym Style is good old traditional weight training; however, Cathe does some really unique moves that really hit the muscles the hardest. Cathe also uses the resistance band in the Gym Styles and I really like Dyna Band training.
You also have some good premix options with the Gym Styles.
But there is a trade-off. The Pure Strength works the abs in two workouts and none of the Gym Styles have an ab workout.
But since you have some workouts that do incorporate abs, that may not be an issue for you.
You can't go wrong with either series, but if I had to pick one over the other, I'd go for the Gym Styles.