Thanks- that wasn’t a search term I used. However having read these posts, it still seems nobody has any clear comparative answers between the different commercial brands. Some people said they’d test and report back but don’t, and others say X is good without knowing how it compares to Y. The best comment is this from over two years ago.
And I’m not sure how keen I am to use mustard as an ink for a product expected to last years! I’m just loath to spend megabucks on any ink that won’t work as claimed. However I’m working on the “you get what you pay for” principle, which unfortunately is closely related to “a fool and his money are soon parted” when people are selling snake oil!