Just received my new macro converters via UPS yesterday and was trying them out this morning. From
My first few tests with the fisheye optic, it would seem that the two converters stacked are too much for the fish eye. I couldn't focus at all and was bumping the front element on what I was focusing on. Next I tried the 16mm and it was still a bit too close. Lastly the 8mm seemed to be the right converter for the fisheye, the front element was about 1/4 inch from the subject.
As for the double glass optic they both worked fine and you are able to get quite close. As of yet I haven't tried the combination of converter and macro lens kit.