I have one now.
Thanks to everyone that replied.

Yes Mike I am very interested, thanks for replying
Offertonhatter - yes i totally agree with you the HD DA AW 1.4x is a quality peice of kit - my Girlfriend purchased one a while ago and uses it with her 100mm f2.8 WR Macro lens and the results are amazing, she is very happy with it but i just cant stretch to the 380 to buy one
I recently borrowed hers to see how well it performed with my K5 and Sigma 150-500 - an overcast day at my local nature reserve and i found that focus locked on everytime at all focal lengths as well as it does without the teleconverter attached and the pictures show no apparent loss of image quality.
Obviously I wouldnt expect a third party teleconverter to perform as well as the pentax offering but it will be good enough for me - I have used the Kenko 1.5x standard screwdrive focus converter with my Sigma 150-500mm on a tripod and manually focusing and the results are very acceptable but i find manually focusing with the Sigma difficult at best.

Hi, I wonder if anyone could help me - i am looking for a 1.4x or 1.5x teleconverter that has the contacts for the HSM and OS on a sigma 150-500.
I wasted £110 on a Kenko 1.5x DG P/AF that i purchased on ebay, the converter had the 2 contacts on the side that mounts to the camera but were absent from the lens side so neither HSM or OS functioned.
My girlfriend has the AW Pentax 1.4x but I am looking for a cheaper alternative, I have limited mobility so the extra reach of 1.4x is much needed
I have available funds and at the moment can travel anytime anywhere
Thanks.