Some of us still have the old Pentax 20-35 F4 designed as a compact wide zoom for film cameras. It had a very limited range for APS-C, but still covered useful focal lengths, was wonderfully compact, and produced marvellous images on the early generation of DSLRs like the 6MP DS. I suspect that may have provided some inspiration for this lens.
I've been with Pentax since buying an MX in 1982, but multiple lens failures have finally persuaded me to move away. The K5 is a fantastic camera - as are the KX, K10 and istDS I owned. But my DA*16-50 was repaired twice, and then literally fell apart, now irreparable. My DA*50-135, while first rate optically, has an SDM so stiff it takes 10 minutes to get going, and will surely fail one day. My little-used DA 12-24 now has a loose front barrel which affects focus, also judged to be irreparable. QC on primes seems good, but on premium zooms, it is unacceptably bad.