There are different regional varieties of black vinegar.
It's umami in a bottle, baby.
www.bonappetit.com
That's why I tried so many brands, in my early days of experimenting with Chinese food! Those two on that link, plus a few others, and the Chenkiang vinegar, which was definitely the best one. Some didn't even have any of the flavor of the rice vinegar. That's what first got me interested in it - some Japanese rice wine vinegar I had gotten in a co-op I was in, which was mild, but a unique flavor.