The differences are listed quickly, the XS is again about 0.5 cm shorter, about 40g lighter, has no metal enclosure, no quick-shift focus and not part of the Pentax Limited Lens series (particularly high-quality production). Optically but it corresponds, both technically (lens number and structure), as well as in practice, the legendary Limited pancake. It is in spite of plastic frame (but metal bayonet) also similarly robust and even in addition to the newer, improved SP-compensation (instead of "only" as in the SMC Limited, see Pentax website) provided.
Whom therefore a somewhat different look this lens does not interfere, which can for Limited here almost de half the money saving (Limited 430 euros) and has a visual equivalent, very sharp fixed focal length. Note, as with all DA lenses only the extension factor 1.5x on a digital camera. That makes this lens the equivalent focal length of 60mm, as well as the Limited, a little less universal in the photo everyday than with analogue systems.