My wife and I stayed in this B&B in June 2022.
We could not have been more delighted! The room we stayed in (Back room) was actually a two floor suite that is probably the best room I've ever had at a B&B. The only possible short coming is that the WC is pretty small - but it's not that big of a deal.
The location is perfect. It's, obviously, right on the Heregracht canal, and in walking distance to the Central train station and the tram. We got around the city for about a week with absolutely no problem. It's also an easy walk to the Jordaan and dozens of restaurants, cafes, and bars.
Finally, Loes and her husband (do note: for some reason the 2020 Rick Steve's guidebook says that Loes is a man, she's definitely a woman) are incredible hosts. Not only did they take immaculate care of the property, they were wonderfully informative about some of the off the radar stuff to do locally. They directed us to several really great restaurants, and helped us take care of some other sundry tasks.
In short, I cannot possible recommend B&B Herengracht 21 enough!