This FL lens is rather compact for a lens of that focal length. The FL lenses were the predecessors of the famous FD series by Canon. I use this tele lens on my FTb QL (on film) or adapted to an EOS DSLR or even my NEX-3. But since you need an adapter with a corrective lens inside when you shoot this lens on an EOS body, the image quality can deteriorate. This adapter especially increases the chance for flares and thus can easily reduce overall contrast of an image. Such an adapter also seems to multiply the focal length by about 1.3.
Despite being a compact lens, it is a pretty heavy one and the built is great, very solid. And the results are very good on film. Even on the 5D (which is some kind of tough test for manual lenses) you can grab convincing images:
So all in all this FL 3.5/135 is a very recommendable lens if you still like to shoot with your old Canon SLR.