Hey, I'm a fresher on the maths and physics course, for me the physics open day wasn't much different from the normal open day, but I found it was heavily focused on being able to look around the department more and ask questions to current students, something that I didn't get a chance to do on the normal open day.
So the open day is best if you still have answered questions or if you want to hear things from a student perspective, but I don't think there was any vital information, they just repeated most of the information from before, but it is always handy to make sure you have the most up-to-date information.
Just ask/pm if you have any questions you would like me to answer about maths+physics or straight physics (I'll try my best)