Hi James.
I've used it a bit on a Pentax K5 and Pentax K1.
When you wrote "With my new beaut Pentax KP I bought an ASTROTRACER unit that fixes on where the flash unit goes." IIS readers not familiar with the Pentax system will get the wrong idea from this statement.
The ASTROTRACER technology is built into the Pentax firmware. However it needs a GPS input for orientation to make the corrections using the sensor shift. The thing you bought and plugged into your flash shoe is an O-GPS1 unit.
My K5 needs the same external O-GPS unit that you have. The K1 has the GPS built in so no external unit is required.
I agree it's great for a quick shot or if you don't have a tracking mount. A well tracked image is still better.
Image at the top of this page is an image I took 2 months ago.
http://joe-cali.com/astronomy/astrophotography-2/
All others on this page are taken with the K5 or K1 but without astrotrace
Another image about 3/4 of the way down this page
http://joe-cali.com/eclipses/PAST/ASE2013/index.html
was also shot with astrotrace 5 mins exposure 12mm f4 lens.
Hope you continue to enjoy the images you are making.
Joe