Q: Target Display mode only with Apple keyboards?

I am unable to use Target Display mode to connect my 2014 Retina MBP to my 2011 iMac. I have searched and read all the "how to's" and the issues with the "use all F1, F2 keys as function keys" thing.

I have the thunderbolt cable. I read on this forum that it only works with Apple keyboards. I have a Logitech keyboard that I downloaded the control panel for and am able to check and uncheck the Function keys thing in their control panel (I am able to increase brightness and other system functions, or not if I check).

All it does when I hit Cmd F2 is beep. Same with Cmd Fn F2. I have tried logging out and it doesn't work in that either.

This is unnecessarily frustrating.