I bought one of these lenses about fourteen months ago second hand but unfortunately because of Covid19 and the lockdown I haven't been able to use it until recently, and although it wasn't cheap it is mint and has the original canon case which is also mint, I paid £260 for it at a local camera store which I think was a steal because I remember that in 1983 when this lens (which was Canon's first L lens ) came out it was £940 and at that time with a wife and two children I definitely couldn't afford it.
I know that 20 -35mm doesn't seem like an very wide focal length range but in use I find for street shooting I can go out with this one lens on my camera instead of lugging my FD 20, 24, 28, and 35mm lenses that saves nearly three and a half pounds in weight for me to carry and avoids the need for lens changes, and the zoom is as far as I can see as sharp and contrasty as my prime lenses, and shooting Fuji Velvia 100 produces sharp, contrasty and saturated colour slides.
I can see many applications for this lens from , parties, weddings, and other indoor social events, to landscape photography.
I'm very pleased with this lens and I don't think anyone who buys one of these lenses in good condition will be disappointed.