Hey findit,
I have been using the Whites PI Pro for about a year.
1. It detects very small items
2. It detects very deep, sometimes deeper than you can dig
3. There is no difference in tone to help you with ID or depth. If you have a beer can at 18 inches, it will sound like a dime at 3.
4. In the surf, when the waves come in, you get lots of feedback. You can tell the difference between a wave and a target, but it does slow you down, causing you to re-scan sometimes if you are not sure.
Good News, it is a very well built heavy duty machine. I have found some larger items at 18 inches plus. I have found pennies at around 10 inches. I have also had to use the probe to find a staple on some occasions. I can't believe it detects that. I have taken it diving and it seems to work just great under water.
Jack