Fitness+ focuses more on metabolic resistance training, which maximizes calorie burn and muscle building in the shortest amount of time. It is not suitable if the primary goal is to bulk up.
References
AF+ is all about metabolic resistance training, it’s meant to be pretty much a 50/50 split between strength and cardio, so if your HR is up that’s just as important as proper form. […] AF+ strength is meant for beginners to burn fat and build a bit of muscle and aren’t experienced with following structured plans.