The 50mm f3.5 Macro lens is THE most popular macro lens ever made. It's cheap, and can double as a standard 50mm lens so a lot of people buy one of these to replace their 50mm f1.8/f2.0 lens that came with the camera. Practically all of them has a 1:2 magnification ratio and they usually came with an extension tube to make the lens capable of 1:1 (life-size) macro shots. Perhaps because of the abundance of these lenses in the used market, they are extremely cheap, usually in the $50-$80 range for a very good condition copy. Naturally, when some people look at it with such low price, they automatically discount the lens as of low quality, or lens snobs who wouldn't look at lenses with an aperture of slower than f2, especially for a 50mm lens :)
I looked at the Minolta version of this lens here, and here, and I liked it a lot, especially when it's so cheap. Last week I got my hands on a like-new Canon nFD 50mm f3.5 Macro, complete with 1:1 matching tube. Leica Guru Erwin Puts has good things to say about this particular lens (can't find the article on his site anymore), so I was itching to try it myself. I was not disappointed.
If you are not a fast lens freak, you will love this lens. Extremely sharp even from maximum aperture of f3.5, and stopping down a little the sharpness will make your eye bleed :) and it's sharp across the whole frame. Very high resolution. At infinity, the sharpness drops a bit, but still excellent.
I find this a very versatile lens to have around. The focal length is comfortable to shoot with, and because it's usable wide open, there really is no restriction except if you need very shallow depth of field. It's worthy of a spot on your lens shelf.
All pictures below were taken with the Sony A7 and Canon nFD 50mm f3.5.