The 285HV is indeed a workhorse. I've used one myself for many years. However, you might also consider the Sunpak Auto 120J (older, discontinued version on the used market) or the current production 120J II.
Neither are as inexpensive as the Vivitar, so budgets do come into play. But I started with the 285HV on my GF670, then moved to a NOS 120J I found and would never go back.
More power (flash meter tested), better quality (softer) light, more power ratio increments, and give-or-take is in the same ballpark in size and weight. That last might be counter-intuitive, but I have held one in each hand. However, YMMV on that.
Best of luck with your decision.
Ken