Kenko/Teleplus 2x tcon

As discussed in the lenses section I recently purchased an as new Kenko 2x to use with my Tamron 70-200mm f2.8 - unfortunately it does not seem to be compatible. I have tried it on my other lenses and it functions on all of them - within the possibilities of slow lenses. On my Sigma non HSM it works perfectly [f2.8/4.5] - on my 55-300 it AFs but very slowly and with much hunting as you would expect on such a slow lens. The good news is that it AFs on my Sigma 55-200mm HSM with little loss of focussing speed - locks focus at f4.5 but as expected hunts at f5.6.
As I no longer have a fast HSM lens or other than the Tamron it seems pointless to keep it.
I paid £75 - open to any reasonable offer! As Sigma don't offer a Tcon that works with HSM in Pentax fit it might make a good cheap alternative!!
Excellent condition, no scratches - more or less as new - both end caps, pouch, box, instructions.

The lens is marked Pz-AF 2X TELEPLUS MC7 KENKO DG.

Update - have now tried it and the Tamron on a K20D and it AFs normally - so it would appear that the non compatability issue of the Tamron is only with the later models.

NOW SOLD