The Metz 60 or 45 potato mashers can only be used in Manual or Auto mode with Canon dSLR, even with the Metz 3102 M3 module, because the flash cannot support the needed pre-flash for ETTL...and the only potatomasher flashes that have this preflash now are the recent version with 'Digital' clearly part of the name, like '45CL4 Digital.
The 45CL is clearly more powerful than the Canon 580EX or Metz 58AF1, if you compare those flashes at the fixed coverage angle of the potato masher, rather than the sleight of hand games that speedlight manufacturers play with the autozoom headed 580EX and 58AF1! The Auto mode of the Metz flashes was wonderfully reliable and consistent in the results, winning the hearts of thousands of wedding pros in the film days, and even today -- in contrast with the inconsistent and unpredictable results with ETTL.
Via the modules, Metz flashes can be made to work with hundreds of models and brands of camera...I can use my Metz with Olympus, Bronica, and Canon simply with a change of module...so I am not locked in to a single brand of camera, and new modules can support newer models of cameras that could be introduced at any time.