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The Vivitar design is unchanged from the 70s. I bought my first Vivitars (263) in 1972 and though the source and quality has changed the design hasn't.
I switched to 285HVs in 2000 when getting my first digital cameras because the trigger voltage on the 263s was too high. I used them for about a year on my 20D when finally cutting the cord to film entirely and getting a DSLR but desided to get a pair of 580ex to do things the Vivitars couldn't, such as HHS and trigger a slave optically without interference from other shootings.
I'd used TTL flash with other cameras previously but the 20D was one of the first Canon bodies to use ETTL-II evaluative zone metering and it was a bit of a learning curve involving a good bit of testing to figure out how it worked and get reliable results with it.
In one test, documented on my tutorial site, I shot a test scene with wide, medium and close-up crops with all 18 different ambient / flash metering combinations. My conclusion? None of them exposed the scene perfectly at EC=0 and FEC=0 when shooting in Av mode and allowing the metering to make all the exposure decisions from it't default "I think this is right" baseline.
To help evaluate exposure I used a white towel and a gray card and noticed that the clipping warning of the camera on the white towel was a good predictor of detail in the highlights in the RAW files. So I changed my approach to flash exosure from thinking in terms of power and distance as I had with the Vivitars to one of taking a test shot at FEC=0, looking at the playback to spot clipping, then adjusting FEC as needed from that baseline. It's not unlike aiming a Canon where a spotter sees how the wind blew the canon ball off target by X amount and calls in the correction to the gunner.
I use the Canon flashes in manual mode and ETTL but use the same "Canon" clipping warning method to adjust exposure. One of the reasons I think the investment in system flashes from Canon or Nikon, depending on what camera brand one uses, it that they offer the option to switch seamlessy from manual, TTL and HHS as needed. The are like three different tools vs. one-trick pony.
For candid shooting with dual flash I usually shoot in ETTL ratio mode. I know from experience and testing that with my Master/fill on bracket and Slave/Key off axis an A:B ratio of 1:2 will record a full range of detail (Master defaults to A so that ratio makes incident strength of key 2x great than fill).
With my diffusers in play I know that FEC=+1-1/3 works most of the time, so that's my starting baseline. I take a shot at those settings and more often than not it's perfect. If the scene is lighter or darker than average it may take 1 or 2 shots to zero in on the ideal exposure based on the clipping warning.
For tasks where the distances are static I switch to manual using the method I learned in the 70s shooting wedding receptions with dual flash. I use identical modifers and the flashes at the same power but if shooting at 8ft I put the slave at 5.6 feet (which happens to be my arm span) from the nose. Due the inverse square law the key light at 5.6ft is 2x brighter (incident) than fill, a 3:1 reflected ratio when they overlap:
1:1 even fill from bracket flash at 8ft shooting distance
2:0 off canera slave at 5.6ft winds up 2x brighter
3:1 Key overlaps fill creating 3:1 reflected ratio the camera records.
When I use that consistent set-up there are no variables and the exposure is always the same. ISO100 @ f/8 when the flashes are set to 1/2 power exposes the highlights perfectly and the lighting ratio exposes the shadow detail perfectly.
The best argument for a system flash vs. manual is that the system flash can do everything the manual flash can, but the system flash can do much more, and the more tools you have at your disposal the more different ways you can solve a photographic lighting problem.
Yes they are more expensive, but they last a long time and over time will be the better investment