The Canon FTb for all intent and purpose is almost identical to the FT QL. However it allows for full aperture metering instead of the stopped down metering of the FT QL, and also was made to work with Canon's FD lens series, which replaced the older FL line up. There is an "on/off" switch on the left top plate to activate the light meter as well. The addition of a dedicated hot shoe is a welcome upgrade for this model.
Here is a link with more information about the FTb: Ken Rockwell FTb Review