The Sigma teleconverters will only fit certain Sigma lenses because they have a protruding front element which fits inside the rear of the 70-200mm f2.8 (for instance). I would say the Tamron 1.4x MC4 is your best bet as Amin has tried mine on his DA* 300mm and it is proven to work.

Or did you get this one which is cheaper but no head?

If you paid £37.95 for the monopod then it should have come with the mini ballhead, mine did.

Value for money and the fact I still remembered when Pentax were as big as Canon and bigger than Nikon.

Well at least he/she got you to post something after 9 months

Im presuming its because it looks like the chap has collapsed in a quivering heap because his camera is not working.

Nobody ever wants to be my friend, count yourself lucky

Have the Tamron 1.4x, Sigma 1.4x EX DG and Pentax 1.7x converters.
The Pentax knocks the spots off all of them even with the extra magnification. If it's for the Bigma though non of them will AF.

The Pentax 1.7x converter works very well with the 300mm primes (I have the older F* 300mm f4.5) but I wouldn't get rid of my Bigma now .. I would miss the convenience of the zoom.

The Pentax is a lot lighter, has a lot less turns to get focus (plus AF) and is more portable .. The Vivitar is sharper, better made and has lovely brokeh. I must admit I was expecting better things from the Pentax but on the plus side I can sell it on and buy another Vivitar with the proceeds.

It means one less lens to carry (maybe 2 if the quality is decent with the 1.7x converter plus I like the idea of being able to go out with my DA* 16-50mm and a DA* 60-250mm with no worry about it raining