Are third party lenses good on pentax k?

Here is what the site says about that.

From Lenses: Third-party lenses: Sigma, Tamron, Samyang and Viltrox make good lenses for many mounts, often for much less than the camera maker's own. Check that the lens supports your body's autofocus features, and that the maker allows third-party lenses on that mount: not every brand does.

From Pentax K: Pentax K: Pentax's DSLR mount since 1975: decades of lenses still fit the current bodies, which have stabilisation built in. Old manual K lenses fit directly.

Quoted from this site's pages.