I tried a bottle of San-J tamari for the first time today. It tasted salty and bitter. I found that adding a pinch of sugar with the tamari to smooth out the bitterness made it taste more similar to soy sauce. But, wanted to get your thoughts? Is tamari and soy sauce a 1:1 substitute?
The answer is both yes, and at the same time no.
The problem is that there are a lot of types of soy sauce (see What are the differences between types of soy sauce? ), and many of them are not good substitutions for each other.
Depending on what type of soy sauce you're replacing, Tamari may be a good 1:1 substitution, or it may not be.