It depend too on which model you are looking at. Like Sandman said, some of the older model have the black seal and do leak. There are basically three models the first two are basically the same except the timing. The newest one on the market is the dual field. each of them are different machines.
I have the PI Pro 8.5 inch "Weighted coil". This coil does not float but can get heavy when working the surf. I was working in a cut just last week with it and pulled a Tiffany ring at about 14 inch deep. On the other hand I went out with it today and pulled out a large junk earring about 20 inches deep.
I don't know if you have ever used a PI machine before, they do go deeper than VLF machines, but they find EVERYTHING...rings, earrings, chains, bracelets, hairpins, papper clips, fish hooks, bolt, screws, pennies, pulltabs, bottle caps, nails, chunks of iron, fishing lures, you name, I have probably dug it up.
I am not familiar with the Tiger Shark, never even seen one, but one thing is for sure, You can beat a machine that has a Lifetime Warranty.
HH
Digger