Older Sigma lenses designed to work with EOS film cameras often needed to be outfitted by Sigma with newer firmware to work with the Canon dSLR, for exampl. Now the newer designs can dock into a special lens dock and firmware downloaded by the user, rather than necessitating a trip back to Sigma...so folks did indeed run into compatability issues with Sigma lense sthat had the EF mount...physical mating did not guarantee it would work!
The trigger I use is not eTTL compatible Pocket Wizard III, as I prefer to manually set flash units when using multiples...I have little inherent trust in eTTL, as I have lost shots all too often simply because of failure of the contacts between flash and hotshoe, spontaneously losing good contact even with a tripod mounted camera unit and shutter triggered with a radio remote nevertheless causing the unit to go into TTL mode (which flashes full power every time).
I actually got my PocketWizards for reliable radio triggering the CAMERA from a distance, rather than as a flash trigger.
I still think Canon put some rookie engineers on the flash design team...why else does External moce (photosensor automation) on a Canon flash underexpose compared to every other photosensor flash in the world?!
I actually have five Metz...
- two 45CT4 which I used in my wedding coverage days with TTL medium format film (ETRSi) in a Main and Filler pair, and which also work with my Olympus OM4 TTL and my Canon dSLR (with flash in Auto) simply by fitting the appropriate Metz module.
- I have two Metz 54MZ4 with eTTL, It, too, has exchangeable control modules, although since I bought them for eTTL compatibility I have had no need yet for other control modules.
- and I acquired an almost new 58AF1 from another POTN member...it will get sold off if I ever depart from Canon system since it is permanently dedicated, unlike any of my other Metz units.]
If my flash trigger does not work with the 58AF1 (which I doubt, if it is merely a trigger, with no eTTL automation), I have two 54MZ4 to use instead. At least I know Metz photosensor exposure is right, unlike using a Canon flash in photosensor mode. I know there are circumstances where photosensor automation can be fooled, untike nTTL flash control. But where I trust my Bronica ETRSi TTL, I do not trust Canon eTTL for its unpredictably erroneous exposure control.
The Metz radio flash control came before Canon's radio flash control, and their radio flash is not compatible....they needed to be radio controllable no matter which brand of camera you used it with.
If I recall correctly, the 58AF1 is Canon radio flash compatible, which makes me wonder about which Pocket Wizard you own 'not compatible with AF2'...what changed in the AF2 so that your Flex TT5 is 'not compatible'?! I would throw that question at Pocket Wizard!
Wireless (radio) triggering has always been a real mishmash of not-compatible systems, part of the reason is trying to be brand agnostic (like PocketWizard and Metz) and because of history (Metz before Canon), and now because of the advent of wireless studio flash units each with their 'our flash is better because of X feature' and needing to support that feature.