[davidmanze]

What is new about the 11-18mm f2.8? Wasn't it released last year?

Funny, that Tamron. Tokina developed a 70-200mm f4 for Nikon F-mount (not for Canon, as Canon had two 70-200mm f4 lenses for years already), and just before it got released... Nikon came with the AF-S 70-200mm f4 VR, resulting in no sales at all for that Tokina.  You'd expect Pentax to take advantage of that situation and just bring that Tokina lens for Pentax. But no.

Lovely lens though, that Tamron. Which goes for €399 (new, Canon EF-mount) currently in my country, and $599 at B&H (LOL @ Pentax price).

 Yes, but the 11-18mm lens passed under most peoples radar (certainly here )..... according to tests it's a little weak in the corners ....... something a ML designed lens probably wouldn't haven't suffered from ....... but overall a sound optic if not too expensive !!
   ........ the Tamron clone is a sad case of re-badging of the most aggressive kind ..... by it's seriously exaggerated price !!

Gone are the days of Pentax offering great value for money !!