Smashburger opened in Mill Valley this past week and I went there today. had their Classic Smash, regular size, $4.99. It was pretty good, fairly juicy with good flavor, if too well done (no choice) for my taste. It seemed to be about a 1/4 pound burger. For $1 more, you get the large one, which I assume is about 1/3 pound. Didn't try anything else. Compared to Super Duper Burger (also in Mill Valley)? It's been too long since I had one to really compare. Neither are my favorite burgers, so I'll reserve my burger calories for Pearl's (Mill Valley) and Phyllis Giant Burgers in San Rafael on the Miracle Mile. As a point of reference so you know who's talking, I don't like In-n-Out at all.
745 E. Blithedale
Mill Valley, CA 94941
415-886-4925 10AM-10PM Daily
A few photos: http://ruthvenphotos2.com/smashburger