The three sizes are perfect beginner sizes. The smallest is about the size of a pinky and probably only needs to be used by someone who has never done any of it before. The middle size is the Goldilocks size; it perfectly hits the prostate and is very comfortable to leave in. The biggest one gives a nice full feeling and still isn't too large, but the curve is past the prostate, so I might prefer to wear a larger plug that wasn't directional if I was to go to go to this size.
Nice graduated sizes, the curved shape is very ergonomic and comfortable. You can wear these while you were doing other things very comfortably. I don't know why all but plugs aren't curve like this because they should be.