I have a Tesoro Tiger Shark with the interchangeable 8 and 10" coils and I have a CZ-21 with an 8 and a CZ-21 with a 10.5" coils. I think BOTH are fantastic machines and BOTH have their place. I hunt at least 4 days a week in Michigan and I have used both over the same spots. I am in a spot almost exclusively that had a huge swim area, a huge "H" shaped dock and two water slides. Because of all the iron nails in the place, sometimes it is almost impossible with both machines to sort out the good from the trash. I have never used a 10" coil here. Just the two machines with the 8".
I find because of the iron that I can sometimes pull silver from the iron with the Tesoro the CZ has missed and vice versa. I think the Tesoro hits nickels deeper as long as you listen to the very faint signals.
I am having a blast at this underwater park. In the last 3 months, I have pulled:
17 Half dollars , 70 Quarters , 152 Dimes , 22 war nickels, and 36 gold from that spot. I haven't even totaled my silver jewelry finds yet.
The Tiger Shark WILL pull silver out of the muck and sand at a foot deep. However, you really have to know the machine and listen. I dive with both machines exclusively.