And as others have said, Andrey, the developer is very responsive. When K2 had it's recent 'hiccup' with Extra Fields not working correctly in the front end editor Andrey was quick to update K2filter too and, on request, provided me with an updated version.
In my opinion this module is superior to the Joomlart one. 2 big winners for me are the ability to have the search results match the original category layout. Not possible in the Joomlart version. And the search box, slider, selector options are more extensive in this one.
Top marks all round.