What I like about this FA J zoom lens: the compact size - its diameter is only a few millimeters wider than 58 mm filter.
What I do't like: plastic lens mount, and no aperture ring.
As shown in the following images, yes, this FA J zoom is the smallest among the three brothers of Pentax FA 28-80 although the FA J at full extension (80mm and 0.4m) is longer than the FA AL, the oldest one.
This FA J lens covers a regularly used focus range, but the lens is not common to find. I do not think that you should have one except for collection.