If what I have read is correct, there were also upgrades to the electronic boards inside it. It was to fix a battery drain issue with some om4 models. The quick test to see if your's is either the old or new circuit, turn the batter check on, and if the steady beep cuts out by itself in ~20 seconds, its the new board.
The f280 flash rocks, I used it at a haunted house we set up for halloween, and I just zone focused with it, and with a high shutter speed, there were some cool reaction results! too bad it blew up and melted on me afterwards. I replaced it with another that cost me only $50 bucks, so not bad. it is also good for daylight fill.