Real people in Unions what are the biggest upsides or downsides compared to non unionized work?

I wanna know from real people who are in unions what the pros and cons are, I worked at Wegmans for 1.5 years and when I started they had an anti union propaganda video and speech that made it seem like they were ran by Satan himself lol, the fact that they were so against it made me wanna start one, only reason I didn’t was because my father was a department manager there.