This is an exceptional macro lenses. It is well known and well respected. The 100mm focal length makes it excellent for portrait photography or macro shots where a 50mm would put you too close to the subject (e.g. insects). All high magnification macro lenses have fairly slow auto focus compared to non-macro versions. The 100mm f2.8 macro can be used for non-macro photography as long as fast focusing is not required.
There are 3 versions of this lens. The original, the RS (re-styled) and the “D” version. All are optically excellent but the newer RS and D version command slightly higher prices. The “D” version provides distance information to the camera body that can improve flash performance.