Rather than making a brash statement, lets learn by actual results. As mentioned above, different levels of different brands will give different results.
I will use my current detectors, that are all at least 12 years old.
Whites XLT: You can adjust anything in the computer, you have preset: turn on and go programs already set, You have program sites for your own custom programs, You have a target ID#, you have a bar that indicates the likely target, You have a pinpointing/ target dept that is exact: that is you can push a probe down in the center of the coil and touch the target, it is that accurate. It has a slide in AA battery pack. It will go down to 2' for a large target, and has no trouble with gold, silver, relics, nuggets etc. Now why do you think I am still using this detector?
Whites Surfmaster PI: What can I say! It has pulled a boat anchof from the sand at app.3', It has pulled a gold/emeral ring from 10" in the sand, It has found the elusive fine gold chain. It has found coins in black sand.
Hays 2 Box detector. I bought it used, It's probably over 12 years also. It will go down over 6' as proven by it's latest find. It will detect 6' sideways to check stone walls as proven by a find. Why would I want to blow more money for a newer one?
The trick is buying high end equipment and taking care of it. it doesn't have to be newer to be better! Just my experience. Frank...
