Just off the top, the Surface Pro 4 has some serious compromises — horse power, ports, and the ability to really use it on your lap come to mind. But in exchange you get a light, fast, high-performance touchscreen device for getting things done.
In lieu of a mouse, it comes with the super great Microsoft Surface Pen stylus for handwriting and precise movements.
Yet, it doesn't really get to "Laptop Replacement" status without the $129 Surface Pro 4 Type Cover. Since the Surface Pro 4 comes with a full, no-holds-barred version of the Microsoft Windows 10 operating system, you need the keyboard to bring it up to its full potential.