I did this back in July of 2019 with a friend. It was a good laugh. That is to say, what I remember of it was a good laugh. I started at noon and managed to get a train home about 12 hours later, so it was a pretty big commitment.
As far as I recall (and that isn’t too far), it was around 15-18 bars or tap rooms. Each with its own brews and guest beers too. Also all of it was craft ale, which I’m not always fond of, but there were a few real stand out beers from that day. One of which was Hiver, a honey beer that I’ve now had several times and just doesn’t disappoint in my opinion.
I would do it again I think. Especially in the summer, when the weather is good and so is the company. Either way, I would thoroughly recommend this, or at least some parts of it. If you’re interested then just look up the Bermondsey Beer Mile in Google Maps. You’ll find everything you need.