I purchased that lens from Amazon more then a year ago and it's been a work horse for me. I bought it for night photography, but have used it for a number of occasions. Most of all, you can't beat the price.
Jack

That shot bring back many, many memories. Had a similar experience with the donkey's of Custer SP. We had our windows open and they tried sticking their heads right inside the car, looking for a handout. The one on my side (driver's side) tried use the side view mirror for a scratching post …… nearly breaking it off.
Jack

Hi Dan,
I can't speak for the 150-600 Sigma, but I have a 150-500 Sigma and I have had no luck at all using a 2x converter with it. Right now my 2x converter is doing nothing more then filling a hole in my camera bag. Having said that, I have heard some good results have been had when using a converter made by Sigma. My suggestion would be to seek out a local Camera Store and try I one out. I noticed your from NH and there is a Hunt's Store in Manchester which I have used often. They have always allowed me to try a piece of equipment before I purchased it.
Jack from Dover