For its price bracket and target audience, the T50 was a very popular and successful model. It was an entry level, automatic exposure only camera for casual photographers buying their first and, perhaps, only SLR. It has all of the levers and pins needed to couple with any FD lens, but was designed to only work with FD lenses. The full range of shutter speeds is only available on the T50 if you mount an FD lens and set the aperture to the green "A." If you take an FD lens off the green "A" setting or mount a non-FD lens, the shutter defaults to a speed of 1/60 and you lose the camera's metering capability. You will only get proper exposure with a non-FD lens (e.g., FL mount, Canomatic R, or a manual aperture/pre-set lens) if the lens is set to the correct, manually determined f/stop for a 1/60 shutter speed for (a) the existing lighting conditions, or (b) for the specific flash unit attached.
With respect to the viewfinder magnification, the FTb and AE-1 are nearly identical (85x vs 86x, respectively). However, the AE-1's viewfinder should be slightly brighter due to its laser matte focusing screen.