Actually I see the DA 10-17mm as a complement to the DA 12-24mm in terms of wide angle coverage.
Even though former is a fisheye and the latter is a rectilinear wide angle, Pentax did put some thought in the angle of view of the two lenses.
The DA 10-17mm has an angle of view of 180 to 100 degrees while the DA 12-24mm covers 99 to 61 degrees of coverage.