wide sigma primes

Hello, another new inexperienced user with fatuous question

I'm interested in purchasing either the sigma 24mm f/1.8 or the 28mm. Was trying to find out if anyone has any experience with these lenses on the Pentax mount, with regard to IQ, usability and build quality (finding it very hard to get objective information on the Internet with regard to lenses.)

I want the lens specifically for landscapes but also with a view to turning round and being able to use it for some walkabout. I'm really taken with using wide lenses for portraits, they seem to add loads of depth (not necessarily dof) against the traditional dreamy telephoto look.

I would be using this to supplement the 18-55 kit and (eventually) the 55-300mm DA or similar.

These look like a good choice for the price and very fast.