Their leaderboards have a ton of stuff, which is great that it's available but can make things hard to find
Leaders -> Pitching -> The year you want
At the very top is a bunch of filters: Starter/Reliever, lefty righty, etc. Between that and the actual list of players you'll see a smaller box, and that has tabs for "Stats" (normal stuff you'd look up) "Pitch Level Data" (velocity, chase rate, etc.) and "Pitch Modeling". Stuff+ lives in that pitch modeling section.
It's a bit silly how tucked away it is. Feels a bit like Dennis Duffy's coffee vending machine.