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Unless you still own an older film EOS camera, having TTL is not necessary. Why? All EOS DSLR use E-TTL (pre-flash metering) since TTL works by metering light reflected off the film emulsion at the moment of exposure and, obviously, TLL won't work with CMOS sensors. If you have a late model film camera like an EOS 3, 1V or Elan 7 series they are compatible with both TTL and E-TTL so an E-TTL only flash should be fine.
One issue I've noticed with aftermarket flash units, even dedicated ones, is the AF assist doesn't work with the outer AF points. Something else to consider.