The 540EZ is not "old school": it is a preferred working tool still extremely common among working professionals for its very high recycling rate compared to later flashes. ETTL is not part of the 540EZ flash specification, only ATTL. ETTL came out with the EOS 3 and EOS 1N V with a beefed-up specification in the latter, and carry-over to Canon's mid-range digital SLRs, of which the EOS 5D is a member. It is perhaps not a wise investment in security to relay on ATTL or ETTL in situations where you know (based on experience) an evaluative or centre-weighted meter can be fooled with supplementary flash, such as mixed or contrasty light. Canon's flash system has braved a lot flack over time, and most of the negative commentary is from users who relay too fervently on system automation then blame the camera for a result they weren't envisioning.