This was my first lens apart from the kit lens. I have never had reason to regret this.
It comes in very handy at many different times but of course landscape and shots of the milkyway are top uses. Beware of scratching the front element as it focuses very close to the sensor. I have also almost walked into things because the field of view is so wide.
On the pentax version the HSM should not be included but most often is. It has only screw drive focus but this fast and not at all noisy. It locks focus easily in dark conditions. From 3 meters to infinity there is only millimeters of travel on the focus dial. No MF button either.
The handling is pleasing with a focus dial that turns easily but not flimsy. The surface is the old velvet like finish.
There is pronounced curvature at 10mm and you better take care to align the front element with your subject or there will be distortions like all.... well.....
Landscape and milkyway pictures are on my page here