DD went to two. At the first she thought she was the only one without parents, and in several cases, extended family. Only parents asked questions and the talk seemed aimed at them. More of the "we are as academic as Oxbridge", nothing on student life. She decided not to apply.
The second struck her as dumbed down. She decided not to apply as it did not seem academic enough. Perhaps the other extreme.
DS went to three. One on his own, which left him enthused. He was always going to prioritise course over anything else, and had already spent time researching academics etc. He was particularly pleased to have had the chance to chat to an academic, specifically on entrance requirements, but presumably other things. (Interestingly they gave different information than the admissions office, about the eligibility of one of his subjects. The academic encouraged him to apply and his offer allowed that subject.)
I went with him to the other two and liked the way students were separated for key subject talks, so students did not have to sit through parent-type questions. (I am sure there is a man in a tweed jacket who does nothing else but attend open days and hurrumph about anti-public school prejudice.) There was so much going on on one campus that we only met up at the car park, but could then compare our impressions. It also meant I could attend peripheral talks, say on taking a year abroad, that DS would not have had time to cover. It was useful to have gone, as DS was not completely sold on living on a campus but might not have had a choice, and I could have reminded him of the upsides.
Almost as useful were self guided tours, though the knowledge of basic facts, entrance requirements, options, of the people designated to answer questions was very variable, and in one case off-putting. "We take anything, General Studies, critical thinking..." and "students used to be able to take options in other departments, but other departments have now decided not to take our students." In contrast, at another University the academic responsible for admissions was free, and in a chat that seemed to include some information gathering from him, he advised which courses at other Universities might suit DS better. (His course, with a year out on a work placement, though highly ranked, was more vocational.) It was useful for DS to gain a better understanding of what he wanted, by considering something he ultimately did not want.