Great bang for the buck
If you are going pro, Nikon or Canon probably are better choices. Pentax lenses are limited and are more expensive. I bought 2 prime lenses (50/1.8 and 35/2.4), they are both very sharp, but the autofocus is not ultrasound. (slow and noisy). They are completely plastic.
1; Great bang for the buck! ($600 for 2 weather-sealed lens, weather-sealed camera body, 1 external flash, a card and a bag) 2; Image quality is very good 3; Good ergonomics, easy-to-navigate menu system; The green button to reset exposure compensation is really nice; 4.
None for the price