It doesn't support pressure sensitivity, a key feature of the other two models. It can attach magnetically on its flat edge and supports hover previews like the second-generation Pencil. However, it can't charge or pair wirelessly via that magnetic attachment like that model can, and it doesn't support the double-tap gesture.
Seems like a waste of money then and not anymore enticing that third party options that existed before. Pressure sensitivity has been the selling point of the Apple pencil.