It's a tiny stall with one guy cooking cockles and mussels. They even open the cockles for you. When I was there, it was raining so the number of seats were really limited. As a result, I had to wait about 15 minutes. After I arrived, the queue got massive and I imagine the wait would have been 30-45 minutes for some. Hopefully it's a different story when it's not raining.
It's a nice little stall with simple fresh seafood and a couple of similar sauces.
Mark Wiens says "Hoy Kraeng Pa Jeen (หอยแครงป้าจิน), a place that specializes in boiled blood cockles and mussels. They are some of the finest shellfish you’ll find anywhere in Bangkok, and this Thai street food stall has been around for over 50 years I believe. It’s an amazing place!"