I have a version of this lens rebranded as a Quantaray (Ritz camera rebrands - but the rear lens cap has the greek letter for sigma printed on the inside
). The lens has a macro capability at 300mm via a switch on the side of the lens. When you zoom to 300mm, you can flip the switch into macro mode. This will allow the lens to focus to about 3 feet, which is half-life size (1:2) at this focal length. This macro capability is ONLY available at 300mm and engaging the macro mode locks the lens at 300mm - you must bring the focus of the lens back to normal (non-macro) range in order to disengage the switch and adjust the zooming of the lens again.
My experience with this lens seems to match the ratings in the third party lens reviews (6.5-7.5/10 rating). Construction is decent overall but the lens is a little weighty due to the metal used in the build. The focus seems a tad sluggish for a screw driven focus lens. At 300mm, the lens is a little soft. Its a fair lens, and since there arent a lot of options for Pentax users for 200-300mm+ this isnt a bad lens option. For $37 Id say you did well (the lens listed for $199-249 new 12 ish years ago - I paid $199 for mine). I dont use mine as much anymore as I find that my 50-135 provides superior image quality cropped compared to this lens up to about 200-225mm, however, if I absolutely need the reach above that point, this lens works out well enough.