It is quite compact, and perhaps that was the primary goal of the design of this lens. The 49mm filter thread goes with many of the OM lenses with the same filter size in that era. The built-in hood is very short and not sufficient to shade the stray lights. It's better than nothing, but not much more.
Optically it's decent, but not earth shattering. I would rank it slightly better than average of the zooms from its days. One thing I dislike of this lens, is that it clips highlights abruptly, as you can see in the picture below, which kind of ruins the feel of the picture.
Is it worth buying one? I probably won't buy one, as I am not really a zoom lens fan, but if you can get it for $20 or so, it's probably good for the occasional day time use when a telephoto lens is needed.
Bokeh - Sony NEX-6 & OM 100-200mm f5 @ f5