The cz-20 is always in salt mode, so it might lag it's sister machines in depth in mild soil....but I am not sure. I suspect all the cz machines have the same circuit architecture, and performance is probably equal across the series. Depth increases with larger coils, generally speaking. Cz's are considered as excellent sensitive machines regardless of coil size.
The czs like iron and will drive you crazy at first. High pitch, then low iron grunt, then high pitch. It took me 2 years to get thru that and learn to just work thru the pesky iron. It doesn't matter, when deep searching, you should run it in autotune mode, but you have to learn the sounds and scrim at first. Deep rusty nails will be dug, the machines give iffy signals on deep iron. I always dig deep iffy signals, hoping for a good one, but the cz rarely lies. Expect nails or corroded Indian cents. Or V nickels.
The cz's give excellent audio feedback concerning depth. On deep silver dimes and cents, you will hear sharp, faint, crisp high pitch tones, so low in volume its amazing. You will know its a coin, and you will be able to guess how deep within 1 inch.
I have dug many hundreds of coins with the cz at 6" or deeper. I have found pull tabs in mild beaches at 12" with 8" coil, in all-metal (autotune) mode.
