Difference between Panasonic and Olympus TTL flash

Hi all,

I have read that Olympus and Panasonic TTL is compatible, so that I can use flashes with Oly TTL on my FZ200. Also many manufacturers sell the same model both for Oly & Panasonic.

But for example Vivitar has different model for Olympus and different for Panasonic. Does anyone know what is the difference between Oly & Pana TTL? Are they totally compatible or only partly compatible?

http://www.vivitar.com/products/9/flashes-and-accessories/1120/df-383

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bYE, Marki