Because you have a Pentax camera body you MUST buy a Pentax 10-17mm Zoom Fisheye.
But for all others reading who may have a Nikon, Canon etc the Tokina 10-17mm Zoom Fisheye is the same lens.
Yes, 6+2 shots to complete a sphere in the usual shooting method.
6x rotational shots at 0 degrees tilt, @60 degree click stops. 1x Zenith shot +90 degrees. 1x Nadir shot -90 degrees.
A better method of shooting would be:
6x rotational shots at -10 degrees tilt down, @60 degree click stops. 2x Zenith shots at +70 degrees tilt up, @180 degrees opposed. 1x tilted tripod offset Nadir shot to cover tripod position. 6+2+1
The Pentax/Tokina is a great fisheye lens with better attributes then that of the Peleng. First it has electrical contacts, so it does communicate with the camera. The Zoom is also a great option, allowing you to shoot higher resolution if needed (of course it will then require more images to cover the sphere). Second it produces an image with less lens flare and is superior with Chromatic Aberration. Third is that you will get correct EXIF data written to the image.
The Samyang 8mm fisheye is also a fine fisheye and far better than the Peleng. But it is a full manual lens with no electrical contacts. You must set everything manually and no aperture information is passed onto the image EXIF data.
Your best option for the Pentax is the Pentax 10-17mm Zoom Fisheye as I recommended in my first reply.