Canon liked to sell cameras at several price and feature levels. In particular, they were good at taking a base model, removing some features, and selling it as a "value-priced" alternative.
In this case, they took an FT, removed the self-timer and lowered the top shutter speed to 1/500th. It was purely for the export market (Europe and the US).
Later on, when they revised the bodies to use their FD mount, this became the TLb.
These were good student cameras, as they're beefy and uncomplicated. Their current value is adversely affected by requiring FL lenses, which means you have to stop-down the camera to the aperture you want when you meter the subject, and adjust the shutter speed accordingly. The later TLbs would allow you to use FD lenses, which meant you could meter the scene wide-open.
For more information: Canon Camera Museum
Camera manual: Orphan Cameras.com