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If you are looking at flashes around $80 new the Yongnuos are a very ggod value. For $100 I got a Neewer flash with the LiOn battery and it is splendid.
The Vivitar is now made as a very non-premum Chinese flash with an old budget name. It is not what it was in the 70's when the original came out as a great value.
That role has been replaced by the growing ranks of decent Chinese flashes with new names like Yongnuo and Godox.
+1. I got one of these years ago and for years it was awesome. Never an issue. It finally died (maybe after 5 or 6 years.) Bought another one and it died after 2 or 3 weddings. They replaced it, and the next one died soon after as well. I'm guessing my first was before the Chinese took them over, and the other ones were after that.
Much better options nowadays. Yongnuo isn't terrible, I have one and it's OK, but I don't love it. I haven't used it, but I hear the LumoPro LP180 is amazing. You might want to check that out.