I think you have already been aware of the promotional bundled products of Surface Pro 4. Microsoft has provided many cool things with the Surface Pro 4 as promotion. The most highlighting offer was the free Office 365 subscription and the free headphones. The same offer is now available for Surface Book too.
If you are now buying a new Surface Book, you will get a free Office 365 subscription and a free Microsoft headset. The offer bundle actually costs $210, but you will now get them with your new device. The deal is valid from 8th September to 21st September. If you are planning to grab a device, this is the right time. Move on now.