David,
I am on a job now with 143 iron pins found so far. The J-Tip has been awesome for me.
I was out with another local surveyor on this same job last Saturday, and he carried his classic Schoenstedt. There were signals that his detector did not really give a definite reading on, that the J-Tip did. There was also a railroad spike 6 inch deep in the road that the J-Tip missed, and his Schoenstedt did find. When I put the J-Tip over his spot, I only had a 1.8 positive reading, which did drop back to zero when I moved away. When the spike was exposed, the J-Tip reading was 11 while in contact with the spike.
I am also getting good at judging depths before we dig in the road. I am usually within an inch.