Finally got around to trying this last night, and left wishing I had been here a lot sooner. By far the best burger I have had in the UK (ok, I haven't been to Meat Wagon/Meat Liquor) but I would imagine it would be up there. The meat is from the Ginger Pig, and is juicy and succulent with a good char on the outside, although was quite salty - they sprinkle the patty liberally with salt when on the grill. Cheese was all gooey and the pickles good and tangy. Comes in a soft brioche bun which has been steamed and was still dewey. Ordered the cheese fries for dessert, they didn't have any chili (might just be a weekend thing).
Despite it getting colder in the evenings, this place is still popular - I hear they often sell out of certain burgers at the weekend so get down early to avoid disappointment.