The Pixel TF-321 adapter for Canon is a quality product with a high Canon-format spec. They have the Canon locking pin and recess and lock securely up and down. But...
The original intent was to provide camera bodies with a Canon ETTL hotshoe but no PC-sync port with an adapter which provided a PC-sync port. Pixel added on top a full hotshoe with three wires connected to provide a pass-through Fire! capability. The problem was that the camera's electronics can be overloaded. Each port (PC, hotshoe) should be independently driven.
So, Pixel cut the three wires to the hotshoe, fixing the loading problem. (The wires are still there and can be re-soldered.) But the unit still had a hotshoe, which now did nothing, but looked as though it might do what many users wanted.
Eventually, Pixel released the "NEW TF-321" which has all 6 wires connected through, and the two ports are correctly buffered. At last, it was what it appeared to be, an ETTL pass-through with a PC-sync port. They also released the TF-326 for Canon, which has no top hotshoe - it is visibly just a hotshoe to PC-sync adapter.
There's more...
Warning: All three versions are currently on sale! The NEW TF-321 at eBay US$14; the old ones at US$9 or up to $39. Let the buyer beware!
Opportunity: The earlier units can be useful. Instead of using sticky tape to cover some TTL pins, just pop on an old TF-321 with 3 wire connected. Professional look. No residue. An instant TTL-Decoupler.
And what about the Kings? The early 3-wire units make a great buffer to drive Speedlites in dumb-flash mode. Canon flash control menus provide either all-ETTL or all-Manual settings. So, the King can only work with these. In fact, the King RX forces all full-featured Speedlites to follow these menu settings, even when the user has set specific values on-flash.
Place a 430EXII on an old TF-321 on top of a King RX, and it will sync, including 2nd-curtain, but its on-flash settings for Flash Mode, Power and Zoom will not respond to menu changes or lens zooming. (A clamp-type adapter or the Mini-Stand would be needed to mount on a light stand as there is no 1/4 socket).





