That is the reason why to check the specs on the pen. The particular pen for the Surface Pro 3 only. The pen itself functions in a dual mode capability but still needs power to do it. It is classed as a "mechanical" pen because it has electronic components.
The two button batteries pre-installed in the top of the pen functions the Bluetooth connection. The main battery actually communicates with the pen's driver installed in the tablet to work with the touchscreen. No digitizer is needed.
If it was a generic pen, you would have an installation disk to install a driver for the pen and that drivers mates with the touchscreen along with adding it as a Bluetooth 4.0 device.
Now, if the Bluetooth connection fails, the pen will still function similar to a stylus where the driver will use the touchscreen like a digitizer surface. The Bluetooth connection is for software control mainly.
It is a little complex but is a great concept in my thought. You eliminate hardware (digitizer) and emulate that hardware with software (driver). Believe it or not, a network adapter and a dial-up modem have been working in that fashion for years; where the driver was actually the modem (simulated hardware) and the hardware (interface card) was just a circuit and connection point.
Right now, you can get Bluetooth and WiFi adapters just slightly bigger than a USB plug. There is only a very small chip in those and rely on the driver to do the rest.
This pen operates in the same fashion. Since the driver for it is built in, it cannot be used with any other tablet and this particular model was designed solely for the Surface Pro 3.
Now, like I said, you can get a generic pen (probably from N-Trig) from their web site. That one will include an installation disk and will work with any tablet that has a touchscreen and Bluetooth 4.0 adapter. You can't with this particular model.