Love the place.
First found Big Red's 2 years ago while back in Madison for a football game and they were selling their goods out of one of those large mobile kitchens.
I fell in love with the cheesesteak in general on a 3 day trip to Philly in 2006 where I ate nothing but cheesesteaks from different vendors for the whole trip (FYI I ended up eating at 4 cheesesteak places and like Geno's the best).
Back to Big Red's, I was very happy when I stumbled upon their cheesesteak cart at around 2am and enjoyed a nice "Whiz with, with mushrooms" (thats phillyspeak for a steak sandwich with cheese whiz, onions and mushrooms). They will yell at you in Philly for ordering inappropriately but not here. The staff was very friendly and willing to chat with you while you wait for your sandwich (can be a while at some times of the night).
I make an honest attempt to stop at Big Red's every time I'm in Madison.