Replaced my Ubuntu 14.10 installation (weird things with video drivers and performance going downhill... basically, time for a rebuild) with Fedora 21 Workstation.
I use a Logitech K810 Bluetooth Keyboard with my laptop (Samsung Series 5 Ultra) when at my desk. And like with Ubuntu it didn't work out of the box (everything else did on Fedora, including suspend! great job Fedora team!).
Reports that this keyboard doesn't work in Linux are hogwash.
Found this article that pertained to Ubuntu: http://programsketches.org/?p=6
For my system I did the following:
mine is hci0, so next I disable ssmpmode:
sudo hciconfig hci0 sspmode 0
To re-enable it, replace the 0 with a 1 in the above command.
Verify that it is disabled:
hciconfig hci0 sspmode
This include the text in the output:
Simple Pairing mode: Disabled
Attempt to pair the keyboard by holding down one of the 3 Bluetooth buttons until it flashes.
Go to Bluetooth settings in the drop-down menu in the upper right of the screen. Connect to the keyboard and a code will be presented to connect the device. Enter that code on the keyboard and your keyboard should be working.