I'm leaving a review for both versions; This is for the 2.4gHz version. It uses the dongle as provided in the hatch on the rear of the remote. Since just about everything has USB, you can take the remote/keyboard and dongle easily and use it with any USB device. The 2.4gHz "pairs" easily with the dongle (hold down F1 while powering on, then releasing it) and on power up it is connect instantly. To get best reception use the extension/charge USB cable to let the dongle rest out front and away from any obstacles.
If you have a PC, or PS4, Bluetooth makes more sense to save a USB slot. If your not worried about using up a USB slot, definitely get the 2.4 gHz one.
This is the review for the Bluetooth version. First off, this version comes with a 2.4 gHz dongle which is completely useless and confusing as it is not compatible with the device--pointless to include it. It is NOT a Bluetooth dongle, let's get that clear. The keyboard will "pair" to ANY Bluetooth device but on many of the most popular android devices, the Bluetooth requires drivers which are not available. It will either connect to your PC and work great or it will say it is connected and do nothing on your android tv box. Also it takes a while to connect on power up, compared to other models which are instant.