Jake, they're absolutely awesome.
I have a group of about 10 (square) ones that I bought on eBay early last year. Apparently I've read they were used as sets in a lecture tour about East End poverty. I've made proper jpegs of all of them by using a lit rostra and a light box (the benefits of working at a museum some of the time).
We used a couple of the shots in TLoJtRTaN, being the Harris's Tobacco Shop shot and the one of Itchy Park. As for the others, as I say, I'll put them up here in due course but I suspect many have not been published. I'm fairly certain the two we used in the book hadn't been.
Tour guides do it loudly in front of a crowd.